Mono No

Outline of Naval Armament and Preparations for War, Part I

145

Outline of Naval Armament and Preparations for War, Part II

149

Outline of Naval Armament and Preparations for War, Part III

160

Outline of Naval Armament and Preparations for War, Part IV

169

Outline of Naval Armament and Preparations for War, Part V

172

Outline of Naval Armament and Preparations for War, Part VI

174

 

Japanese Monograph No. 145

OUTLINE OF NAVAL ARMAMENT AND PREPARATIONS FOR WAR

Part I

PREPARED BY MILITARY HISTORY SECTION HEADQUARTERS, ARMY FORCES FAR EAST

DISTRIBUTED BY OFFICE OF THE CHIEF OF MILITARY HISTORY DEPARTMENT OF THE ARMY

This is the first of a series of six monographs in regard to Japan's naval armament in preparation for and during the Pacific War.

Additional monographs covering Japan's naval armament plans are:

Mono No

Outline of Naval Armament and Preparations for War, Part II

149

Outline of Naval Armament and Preparations for War, Part III

160

Outline of Naval Armament and Preparations for War, Part IV

169

Outline of Naval Armament and Preparations for War, Part V

172

Outline of Naval Armament and Preparations for War, Part VI

174

--iii--

Preface

Through Instructions No. 126 to the Japanese Government, 12 October 1945, subject: Institution for War Records Investigation, steps were initiated to exploit military historical records and official reports of the Japanese War Ministry and Japanese General Staff. Upon dissolution of the War Ministry and the Japanese General Staff, and the transfer of their former functions to the Demobilization Bureau, research and compilation continued and developed into a series of historical monographs.

The paucity of original orders, plans and unit journals, which are normally essential in the preparations of this type of record, most of which were lost or destroyed during field operations or bombing raids rendered the task of compilation most difficult; particularly distressing has been the complete lack of official strength reports, normal in AG or G3 records. However, while many of the important orders, plans and estimates have been reconstructed from memory and therefore are not textually identical with the originals, they are believed to be generally accurate and reliable.

Under the supervision of the Demobilization Bureau, the basic material contained in this monograph was compiled and written in Japanese by former officers, on duty in command and staff units within major units during the period of operations. Translation was effected through the facilities of Allied Translators and Interpreters Service, G2, General Headquarters, Far East Command.

--v--

This Japanese Operational Monograph was rewritten in English by the Japanese Research Division, Military History Section, General Headquarters, Far Bast Command and is based on the translation of the Japanese original. Editorial corrections were United to those necessary for coherence and accuracy.

--vi--

TABLE OF CONTENTS

Page

Chapter I

Period Between Washington Conference and First London Conference

1

Vessel Armament

2

Air Armament

5

Chapter II

First Naval Armament Replenishment Plan

11

Vessel Armament

11

Air Armament

12

Chapter III

Second Naval Armament Replenishment Plan

17

Vessel Armament

18

Air Armament

19

Appendix I

Negotiations between the Navy Ministry and the Navy General Staff regarding the First Naval Armament Replenishment Plan

23

Appendix II

Navy General Staff Secret Document No. 154

47

Appendix III

Outline of Second Naval Replenishment Plan

59

Appendix IV

Disposition of Air Units after Completion of Plan 2 - End of 1936

61

 

 

Chart No. 1

Naval Strength at end of 1924

3

Chart No. 2

Naval Strength - 30 September 1930

6

Chart No. 3

Organization of Air Groups - 1 November 1942

8

Chart No. 4

First Naval Armament Replacement Program 1931 Program

13

Chart No. 5

Vessels Constructed from 1931 to 1933

14

Chart No. 6

Plan 1 - Distribution of Air Strength in Normal Situation

16

Chart No. 7

Dates of Completion of Major Vessels Built under Program 2

20

--vii--

CHAPTER I

Period Between Washington Conference and First London Conference

The Washington Disarmament Treaty was concluded on 6 February 1922. It was foreseen that the effect of this pact would be to greatly weaken the Imperial Navy, consequently naval authorities mapped out plans to overcome these weaknesses by replenishing their strength with naval vessels outside treaty restrictions, as well as by building up air strength.

Each year the Navy submitted proposals and made requests for budgetary allocations. However, from 1922 to 1924, Japan, honoring the Washington Treaty, continued to scrap vessels and make the other modifications provided for in the treaty. At the same time, the Imperial Navy voluntarily undertook the reduction and modification of the auxiliary building program based on the 8-8 Fleet Plans (Plans to keep 8 BB and 8 BC as its fleet's nucleus.) Subsequently, because of the tremendous financial burden placed on the country by the Great Kanto earthquake, the Imperial Navy was forced to postpone the dates of completion of all armament plans. The long-term plan for naval shipbuilding extending from 1911 to 1927 was repeatedly reduced and postponed for financial reasons and rarely got past the planning stage. Naval air power also suffered a considerable setback because of the national trend toward financial retrenchment and disarmament.

--1--

During this period of inertia in naval rearmament even the number of cadets accepted for the Naval Academy was drastically reduced. In 1923 only one-sixth of the 300 students planned for under the 8-8 Fleet Plan were accepted.

Vessel Armament

The period from 1922 to 1924 was regarded as the readjustment period in accordance with the provisions of the Washington Disarmament Treaty.

The Washington Treaty referred to battleships and battle cruisers as capital ships and all other naval vessels as auxiliary ships. In regard to capital ships, ten were to be retained, while ten ships ranging in age from 10 to 20 years, together with six ships under construction and eight still in the planning stage were to be scrapped, disposed of, or maintained for noncombat purposes.

The tonnage of aircraft carriers was so far below the 81,000 maximum that the Kaga and the Akagi were to be reconstructed as aircraft carriers.

Since auxiliary ships were limited only in displacement tonnage and in the caliber of guns, the construction program for such craft was extended by constantly putting off prearranged plans. A Naval strength at the end of 1924, when the readjustment and scrapping of vessels in accordance with the Washington Treaty was completed, was as shown in Chart 1.

--2--

Chart 1 — Naval Strength at end of 1924

Classification

Number of Ships

Total
Standard
Displacement

Battleships

6

184,062 tons

Battle Cruisers

4

105,280 "

Total for Capital Ships

10

289,342 "

Aircraft Carriers

2

12,650 "

Second-class Cruisers

18

82,855 "

Destroyer Tenders

4

21,015 "

Mine Layers

3

17,960 "

First-class Coast Defense Ships

7

59,410 "

Second-class Coast Defense Ships

4

13,615 "

First-class Gunboats

4

4,393 "

Second-class Gunboats

9

2,915 "

First-class destroyers

30

35,495 "

Second-class Destroyers

51

37,510 "

Third-class destroyers

2

640 "

First-class Submarines

1

1,400 "

Second-class Submarines

39

30,842 "

Third class Submarines

10

3,259 "

Special Service Ships

29

292,488 "

Total for Auxiliary Ships

213

616,447 "

GRAND TOTAL

223

905,789 tons

--3--

From 1925 until the London Disarmament Conference in 1930 it was possible to carry out only a minimum amount of construction. The armament program was constantly reduced and the established continuous building program was postponed due to financial difficulties. During this period no new replenishment program was approved by the Diet. Ships actually completed from 1925 to 1930 were as shown hereunder:

Year

Type

Name of Ships

1925

Cruisers

Abukuma, Jintsu, Naka

Destroyers

Yunagi, Oite, Satsuki, Kisaragi, Hayate

Submarines

Three ships

1926

Cruisers

Furutake, Kako

Destroyers

Mutsuki, Fumisuki, Yayoi, Uzuki, Kikuzuki

Submarines

Five ships

1927

Aircraft carrier

Akagi

Cruisers

Aoba, Kinugasa

Destroyers

Minatsuki, Nagatsuki, Mikazuki, Yuzuki, Nechizuki

Submarines

Seven ships

1928

Aircraft carrier

Kaga

Cruiser

Nachi

Destroyers

Isonami, Shinonome, Usugumo, Shirakumo, Fubuki, Shirayuki

Submarines

Four ships

1929

Cruisers

Haguro, Myoko, Ashigara

Minelayers

Shirataka, Itsukushima

Gunboat

Atami

Destroyers

Natsuyuki, Murakumo, Miyuki, Uranami, Shikinami

Submarines

Five ships

1939

Minelayer

Yaeyama

Gunboat

Futami

Destroyers

Ayanami, Asagiri, Amagiri, Yugiri

Submarines

Three ships

The strength of the Imperial Navy on 30 September 1930 was as shown on Chart 2.

The London Treaty for limitations of auxiliary naval vessels was signed on 22 April 1930 and ratified by the Emperor on 2 December 1930. As a result of this treaty, Japan agreed to limit her tonnage to:

A-class cruisers

108,400 tons

B-class cruisers

100,450 tons

Submarines

52,700 tons

The Japanese Navy decided that the obsolete auxiliary vessels, the Aso, Tokiwa, Asama, Yagumo, Izumo, Iwata, Kasuga and Yodo would be treated as special ships outside tonnage limitations, while the Hiei and three cruisers of the Kuma class would be retained as training vessels.

Air Armament

The Japanese Imperial Navy began using aircraft in 1912. However, in spite of their using aircraft aboard the Wakamiya Maru to great advantage in the invasion of Tsingtao during World War I, development of naval aviation was very slow. It was not until 1916 that, together with the organization of the Yokosuka Air Group, a plan for organizing three air units was approved by the Diet with the necessary appropriations. The Sasebo Air Group was established in 1918, and the same year a plan was formulated to add five more air units, bringing the total to eight

--5--

Chart 2 — Naval Strength - 30 September 1930

Classification

Number
of
Ships

Total
Standard
Displacement

Battleships

6

184,080 tons

Battle Cruisers

4

111,320 "

Total for Capital Ships

10

295,400 "

Aircraft Carriers

4

66,450 "

First-class Cruisers

8

68,400 "

Second-class Cruisers

21

98,415 "

Submarine Tenders

4

21,015 "

Mine Layers

5

21,275 "

First-class Coast Defense Ships

7

59,410 "

Second-class Coast Defense Ships

2

6,630 "

First-class Gunboats

2

2,045 "

Second-class Gunboats

11

3,255 "

First-class Destroyers

54

75,125 "

Second-class Destroyers

48

35,070 "

First-class Submarines

22

34,788 "

Second-class Submarines

45

36,185 "

Mine Sweepers

10

7,290 "

Special Service Ships

25

266,798 "

Total for auxiliary Ships

270

802,151 "

GRAND TOTAL

280

1,097,551 tons

--6--

units. In 1920, the plan was increased by a further nine air units, raising the total to 17 units.

The importance of aeronautics was recognized by the Japanese Imperial Navy in 1921 to the extent that upon the advice of a group of highly proficient aeromechanics from Great Britain, drastic changes were made in the method of developing aeronautical techniques. However, the organizational system and technical and military strength of aviation, as well as the over-all setup still failed to meet the requirements of the Navy's plans for building up its forces. Therefore, the execution of the plan for establishing the 17 air units, as well as replenishment of such forces, was delayed until 1930.

At the conclusion of the Washington Disarmament Treaty in 1922, the Imperial Navy was confronted with a situation wherein it was found necessary to reinforce its air strength and make qualitative improvement in armament, along with the replenishment of auxiliary vessels. It selected promising young men and made every effort to bring its air force up to full strength. It drew up and issued an order for the organization of naval air groups on 8 October 1924, to be effective on and after 1 November 1924 (See Chart 3).

In this way the ground work was laid for the building up of air power. The actual replenishment of the air forces, however, did not go beyond the stage of reinforcing end modifying its strength by one and a half units a year, due to the extremely low production of aircraft and the inferiority in techniques and performance, as well as

--7--

Chart 3 — Organization of Air Groups - 1 November 1942

Unit Designation

Classification of Aircraft

No
of
Air
units

Yokosuka Air Group

Airplanes

Seaplanes

Reconnaissance Planes

1.0

Flying Boats

0.5

Carrier Planes

Attack Planes

1.0

Balloons

1.0

Total

3.5

Kasumigaura Air Group

Airplanes

Seaplanes

Reconnaissance Planes

1.0

Training Planes

0.5

Carrier Planes

Reconnaissance Planes

1.5

Land Planes

Training Planes

2.0

Research Planes

1.0

Dirigibles

1.0

Total

7.0

Sasebo Air Group

Airplanes

Seaplanes

Reconnaissance Planes

1.0

Flying Boats

0.5

Total

1.5

Air Group

Carrier Planes

Fighters

1.0

GRAND TOTAL

13.0

Composition of an air unit is fully described in Monograph No. 169.

--6--

to the length of time necessary to train personnel.

By the end of 1930 seventeen units had been organized. These units were designated the "Old Aerial Armament Program" and came under a different classification from units under the first replenishment program. Disposition of these units was made as follows:

Type

Yokosuka

Kasumigaura

Tateyama

Sasebo

Omura

Total

Primary training planes

3.0

3.0

Carrier fighters

0.5

0.5

1.0

2.0

Carrier reconnaissance planes

0.5

1.5

2.0

Carrier attack planes

6.5

1.0

1.0

2.5

Reconnaissance seaplanes

0.5

1.5

1.0

1.5

4.5

Flying boats (small)

0.5

1.0

0.5

2.00

Research planes

1.0

1.0

Total

2.5

7.00

3.5

2.0

2.0

17.0

In addition, one dirigible unit was attached to the Kasumigaura Air Group, Considerable changes in the organization and distribution of aircraft was expected with the establishment of new air groups and the reinforcement of aircraft.

The total number of aircraft available in the 17 units was 284 planes, of which 109 were reserve planes.

--9--

CHAPTER II

First Naval Armament Replenishment Plan

As a result of the London Naval Disarmament Treaty, the Japanese Imperial Navy was permitted to have, in gross weight, almost as much tonnage as it had demanded from Great Britain and the United States. In substance, however, the "A" class cruisers were reduced to a tonnage of about ten percent less than its demand in ratio to the United States Navy, and the submarines were reduced to approximately 25,000 tons in absolute weight.

Having regard to these limitations, the Navy keenly felt the necessity to build the tonnage specified in the treaty as promptly as possible, and also to expand air armament beyond the limit of the treaty. On 7 October 1930, the Navy Minister presented the Prime Minister with a new plan for a complete readjustment and replenishment of major naval strength. The plan, slightly modified, received the approval of the Diet in 1931, end was known as the First Naval Armament Replenishment Plan, or simply as Plan 1. The budget for this plan passed the Diet for a period of six years from 1931 to 1936 totaling 424 million yen. (¥2.5 = $1) (Details of the negotiations conducted between the Navy Ministry and the Navy General Staff regarding the First Naval Armament Replenishment Plan are shown in Appendix I.)

Vessel Armament

The First Naval Armament Replenishment Program included a plan

--11--

to construct 39 vessels with a total tonnage amounting to 72,905 tons, at an expenditure of 247,080,000 yen over six years from 1931 through 1936. (Chart 4) This plan was to be carried out through the redistribution over the six-year period of the budget originally allocated for the construction of auxiliary vessels under the continuous program. By the end of 1933, 25 vessels totaling 74,789 tons had been completed under this program. (Chart 5) Following the Tomozuru Incident in March 1934 and the 4th Fleet Incident in September 1935, it became necessary to make revisions in the designs of some of the vessels to improve their efficiency and strengthen their hulls. The completion of the plan, therefore, was delayed until the end of October 1937.

In 1933 a budget of 15,000,000 yen was passed for the plan known as the 1933 Program, apart from Program I, to construct the submarine tender Taigei and two Class "A" subchasers. Construction on the 10,000-ton tender Taigei was started in April 1933 and completed in March 1944, while construction on the two 300-ton subchasers was started in June 1933, end in March 1944 they too were completed.

Air Armament

In Plan I the Navy General Staff originally had asked for 28 air units. During the course of negotiations with the government, however, this was reduced to 16 unite. Moreover, appropriations for this plan were made on the condition that the construction of two

--12--

Chart 4 — First Naval Armament Replacement Program

1931 Program

Category

Number

Tonnage
per
Vessel

Total Tonnage

Class of Vessel

Date of Commencement

Date of Completion

2d Class Cruiser

4

8,500

34,000

Mogami Class

Oct 31

Oct 37

Destroyer

12

1,368

16,416

Hatsuharu Class 6

May 31

Aug 37

Shiratsuyu Class 6

Submarine

1

1,900

Long Cruising Range

Jun 31

May 37

"

6

1,400

Large size

"

"

"

2

700

11,700

Medium size

"

"

Minelayer

1

4,400

4,400

Okinoshima

Sep 34

Sep 36

Torpedo Boat

4

527

2,108

Chidori Class

Oct 31

Jul 34

Minesweeper

6

492

2,952

No. 13 class

Dec 31

Apr 36

Auxiliary Minelayer

3

443

1,329

Natsushima Class

Dec 31

Sep 34

TOTAL

39

72,905

--13--

Chart 5 — Vessels Constructed from 1931 to 1933

Year

Name of Vessel

Displacement
Tonnage

Commencement
of
Construction

Completion

1931

Sagiri

1,700 tons

28 Mar 29

31 Jan 31

Akebono

1,700 "

25 Oct 29

31 Jul 31

Obore

1,700 "

29 Nov 29

31 Oct 31

Ushio

1,700 "

24 Dec 29

14 Nov 31

1932

Takao

9,850 tons

28 Apr 27

31 May 32

Atago

9,850 "

28 Apr 27

30 Mar 32

Chokai

9,850 "

26 Mar 28

30 Jun 32

Maya

9,850 "

4 Dec 28

30 Jan 32

Yaeyama

1,135 "

2 Aug 30

31 Aug 32

Ikazuchi

1,700 "

7 Mar 30

15 Aug 32

Bazanami

1,700 "

21 Feb 30

19 May 32

Akatsuki

1,700 "

27 Feb 30

30 Nov 32

Inazuma

1,700 "

7 Mar 30

15 Nov 32

Submarine I-5

1,950 "

30 Oct 29

31 Jul 32

Submarine I-65

1,638 "

19 Dec 29

1 Dec 32

Submarine I-66

1,638 "

8 Nov 29

10 Nov 32

Submarine I-67

1,638 "

14 Oct 29

8 Aug 32

1933

Ryujo

7,400 "

26 Nov 29

9 May 33

Hibiki

1,700 "

21 Feb 30

31 Mar 33

Hatsuharu

1,368 "

14 May 31

30 Sep 33

Nenohi

1,368 "

15 Dec 31

30 Sep 33

Chidori

527 "

13 Oct 31

20 Nov 33

Minesweeper 13

492 "

22 Dec 31

31 Aug 33

Minesweeper 14

492 "

22 Dec 31

30 Sep 33

Natsushima

443 "

24 Dec 31

31 Jul 33

--14--

air units be postponed until the 1938 fiscal year or later. This meant that only 14 units would actually be activated by the end of 1936. At that time demands for government appropriations for air armament were not made on the same concrete numerical basis as budgetary demands for the construction of vessels. Considerable difficulty was involved in obtaining aircraft equipment and in the improvement of necessary airfield facilities. The situation was such that even the drastically reduced plan was not completed until the end of October 1937.

The type of aircraft required under Plan I were:

Carrier-borne fighters

2.0 units

Carrier-borne attack planes

6.0 units

Reconnaissance seaplanes

1.5 units

Medium size flying boats

3.0 units

Large size flying boats

1.0 units

Test planes

0.5 units

Total

14.0 units

One hundred and seventy-six (176) planes were required, of which 46 were to be used as replacements.

Because of their frequent transfers, the distribution of the air units among the various air groups cannot be clearly stated. However, in view of the time of establishment, size of the airfields, and their convenience for training, Chart 6 is considered sufficiently correct to show the distribution of air strength in normal situations.

--15--

Chart 6 — Plan 1: Distribution of Air Strength In Normal Situation

Type of Plane

Yokosuka

Kasumigaura

Tateyama

Yokohama

Ominato

Kure

Sasebo

Omura

Saeki

Total

Old
Program

Grand
Total

Primary trainer

0

3.0

3.0

Carrier-borne fighter

0.5

0.5

0.5

0.5

2.0

2.0

4.0

Carrier-borne

reconnaissance

plane

0

2.0

2.0

Carrier-borne attack plane

2.0

0.5

1.0

0.5

0.5

1.5

6.0

2.5

8.5

Reconnaissance Seaplane

0.5

0.5

0.5

1.5

4.5

6.0

Small-size

flying boat

0

2.0

2.0

Medium-size

flying boat

1.0

1.0

1.0

3.0

3.0

Large-size firing boat

1.0

1.0

1.0

Teat plana

0.5

0.5

1.0

1.5

Total

3.5

1.0

2.5

1.0

0.5

2.0

1.0

0.5

2.0

14.0

/

/

Old Program

3.0

7.0

2.5

0.5

1.5

2.0

0.5

/

17.0

/

Grand Total

6.5

8.0

5.0

1.0

1.0

2.0

2.5

2.5

2.5

/

/

31.0

--16--

Japan's foreign relations, which had been deteriorating since the Manchuria Incident, grew worse after her withdrawal from the League of Nations. In view of the forthcoming Disarmament Conference and the expected trend in international affaire, it seemed as though the security of the whole of East Asia would depend upon the real power of Japan. Moreover, with the huge increase in American naval forces, culminating with the first Vinson Program in March 1934, Japan felt a very urgent need to replenish her naval forces. Despite the fact, therefore, that Plan 1 was still in progress, it was decided to put into operation the Second Naval Replenishment Plan, called Plan 2, in order to replenish the naval forces up to the treaty limits at the earliest possible moment. This replenishment program was to be completed in four years from 1934 to 1937. The Navy Minister negotiated with the Finance Minister on several occasions concerning budgetary appropriations for the program, and finally the program was approved by the Cabinet and submitted to the Diet. The budget for the program was set at 477,127,300 yen (¥ 4 - $1) of which 431,688,000 yen was to be used for ship construction, and 45,439,300 yen for creating eight air units. This received Diet approval and, with the Imperial Sanction, was published as law on 20 March 1934. (Appendix II shows communications between the Navy Minister and the Navy General Staff relative to Plan 2, and sets forth the Navy General Staff's requirements to fulfill their proposed plan.)

Vessel Armament

In Plan 2 the Navy General Staff originally asked for an additional 87 ships with a total displacement of 159,370 tons, to include 22 ships of 63,200 tons under the treaty limitations. However, they could not win the full approval of the Finance Ministry in regard to the construction of vessels outside the treaty limitations, although the plan to bring up to maximum strength the vessels coming under the treaty limitations met with little objection from other government agencies.

After prolonged negotiations the Navy was forced to reduce this armament program to a four-year program, in which time they were to build 43 vessels with a total displacement of 137,350 tons. A budget amounting to 431,688,000 yen was finally passed by the Diet for this program. (Outline of the Second Naval Armament Replacement Program is shown in Appendix III.)

A number of ships scheduled in Plan 2 had their keels laid in the latter half of 1934, however, the construction of the Hiryu, Chikuma and Takasaki had to be postponed about one year, mainly because of a shortage of dockyards. This same difficulty was met in the case of destroyers, although the urgent necessity to improve their equipment was realized after the Tomozuru accident.

The tremendous damage suffered by the Fourth Fleet in a typhoon

--18--

in the fall of 1935 clearly showed the necessity for drastic improvement in the construction of all naval vessels. Not only were sweeping changes made in design of all ships under construction, but it was necessary to strengthen almost all ships already commissioned. This, coupled with the execution of the existing plan for remodeling capital ships, caused a rapid increase in naval construction, but at the same time, served to delay the completion of Plan 2 to a very great extent. (Chart 7)

Air Armament

With the completion of the aircraft carrier Ryujo in May 1933, in addition to the Hosho, Kaga and Akagi. the carrier-borne air force acquired great importance as the Navy's main offensive unit. At the same time, aircraft carried by battleships and cruisers also gained in importance as essential means of spotting, scouting and contact. This resulted in a revolutionary change in the concept of sea operations and, with the increasing cooperation of the land-based air force, sea operations in the form of patrol and attack sorties helped greatly to contribute to the idea that aircraft was of tremendous importance in carrying out such operations.

Plan 2 made provision for only eight new units, however, appropriations were made to carry out the reorganization of nine units, and also to move up the completion date of the ten Diet-approved units to the end of the 1936 fiscal year, which was the deadline for the completion of Plan 2. By the end of the 1936 fiscal year,

--19-

Chart 7 — Dates of Completion of Major Vessels

Built under Program 2

Type

Name

Date of Completion

Months Delayed

Remarks

Aircraft Carrier

SORYU

29 Dec 37

"

HIRYU

5 Jul 39

16

Cruiser

TONE

20 Nov 38

8

"

CHIKUMA

20 May 39

14

Destroyer

UMIKAZE Class: 4

31 Aug 37
last ship

"

ASASHIO Class: 10

28 Jun 39
last ship

15

Submarine

Cruising Submarine: 2

5 Dec 38
last ship

9

"

Large Size: 2

18 Dec 38
last ship

9

Seaplane Tender

CHITOSE Class: 2

15 Dec 38
last ship

9

"

MIZUHO

25 Feb 39

11

Submarine Tender

TSURUGIZAKE

15 Jan 39

10

Work for conversion into an aircraft carrier begun about Nov 40, finished Dec 41.

Submarine Tender (aircraft carrier)

TAKASKI

27 Dec 40

33

In the course of building this ship was converted into an aircraft carrier. Finished on 27 Dec 40.

--20--

therefore, the total number of units was to be 39. The eight new units would comprise:

Carrier-borne fighters

3.0 units

105 planes (including 25 planes for replacement.)

Medium attack planes

2.5 units

Large attack planes

1.5 units

Large flying boats

1.0 units

The disposition of the air groups, upon the completion of Plan 2, was provisionally scheduled as shown in Appendix IV.

Only four of the eight land-air groups were completed by the end of the 1936 fiscal year. The completion of the four remaining groups was delayed more than a year. There was from one to two years' delay in the completion of the program for carrier-borne and shipborne aircraft.

Due to the delay in obtaining aircraft material, two of the two and a half units of medium attack planes were not completed until the end of the 1937 fiscal year.

It was only with great effort that a half unit of the 1 1/2 large attack-plane units was completed by the end of the 1936 fiscal year. The performance of this aircraft (Type 95 land-attack planes) was extremely low, and they were completely expended through mishaps during the China Incident before the tactical value of the unit could be shown. The production of this type of plane was discontinued, and, at the same time, an attempt was made to improve the performance of medium attack planes. The execution of the plan for armament of large attack planes was left in abeyance until the middle of World War II, when plans were made for the production of the "Renzan" bombers.

--21--

Despite the fact that the aircraft complement for a flying boat unit was only two aircraft per unit, the completion of one flying boat unit was delayed almost a year due to materiel shortages.

The delay in naval armament caused a delay in the equipment and organization of carrier-borne and shipborne planes from one to two years. With the exception of the special cases stated above, Air Armament Plan 2 was completed by the end of the 1937 fiscal year — about one year after the specified date of completion. The total number of aircraft and personnel at the end of the 1936 and 1937 fiscal years was:

1936 fiscal year

1937 fiscal year

Crews

Planes

Crews

Planes

Land air groups

1,620

519

1,810

563

Carrier-borne and ship-borne planes

701

261

901

332

TOTAL

2,321

780

2,711

895

--22--

Appendix I

Negotiations between the Navy Ministry and the Navy General Staff regarding the First Naval Armament Replenishment Plan

On 27 June 1930, the Chief of Naval General Staff sent the Navy Minister a note with basic recommendations on the replenishment of strength following the London Naval Treaty. Simultaneously, the Vice Chief conferred with the Vice Minister regarding details. On 8 July 1930, the Minister replied to the effect that he would endeavor to realize the complete adjustment and replenishment of strength as far as general conditions, especially the financial situation, would allow. On 11 September 1930, the Chief of the Navy General Staff forwarded to the Navy Minister, Navy General Staff, Secret Document No 176, stressing the need for naval strength. In response to this correspondence the Navy Minister pushed the study of the recommendations and at the same time carried out negotiations with the government in order to obtain the necessary appropriations. On 15 November 1930 the Navy General Staff received a reply from the Navy Ministry stating that owing to the unfavorable state of the national finances the appropriation requests had been cut. It also gave the appropriations to be made to the Navy, and the measures to be taken by the end of 1936 in order to minimize the shortage in strength after the treaty had gone into effect.

--23--

Navy General Staff Secret Document No 176

11 September 1930

From: Chief of the Navy General Staff, TANIGUCHI, Naomi

To: The Navy Minister, TAKARABE, Takeshi

Subject: Recommended plans for construction and replenishment of naval vessels and for the replenishment and expansion of air strength

The above mentioned plans, the contents of which are shown in the appended sheet, were drawn up by the Navy General Staff after careful study, with a view to minimizing tactical handicaps arising from the armed strength agreed upon in the London Naval Treaty. These plans, agreeing in principle with the Reply to the Throne made recently by the Supreme War Council, are absolutely indispensable from the standpoint of national defense and strategic operations. In the light of the strength of naval forces of the major powers subsequent to the conclusion of the London Naval Treaty, and in view of the current naval rearmament of the Empire and future developments, it is considered most imperative from the view of national defense to carry out the replenishment program recommended previously in Navy General Staff Secret Document No 116 of 1930. Such being the case, your efforts toward the completion of these plans upon the conclusion of the London Naval Treaty will be greatly appreciated.

The gist of the Appendix to Navy General Staff Secret Document No 176:

The plan for construction and replenishment of naval vessels (abridged)

--24--

Most effective use is to be made of the forces which the Empire is permitted to retain under the new London Navy Treaty. Efforts are to be exerted toward replenishment of naval vessels not restricted by the treaty.

These plans are to be put into execution during the 1931 fiscal year and completed by the end of the 1936 fiscal year. The construction of ships begun about this time, and restricted by the treaty, is to be completed by the end of December 1936. However, the construction of those ships permitted by the treaty to be under construction at the end of 1936, as well the construction as those ships not restricted by the treaty, is to be begun in 1934 and completed by the end of the 1938 fiscal year.

Replenishment and construction of naval vessels Ships Limited by Treaty

Category

Standard
Displacement
Tonnage

Number
of
Ships
to
be
Constructed

Number
of
Ships
to
be
Started
in
1934

Cruisers

8,500

4

2

Aircraft Carrier

9,850

1

0

Destroyers

1,400

18

7

Submarines

1,900

1

2

1,400

6

2

700

2

0

Remarks

1,900 ton submarine is long cruising range type.

1,400 ton submarine is Navy-type large.

700 ton submarine is medium type.

--25--

Ships Outside Treaty Limitation

Category

Standard
Displacement
Tonnage

Number
of
Ships
to
be
Constructed

Number
of
Ships
to
be
Started
in
1934

*Coast-defense ships

1,200

4

0

Gunboats

900

2

0

200

1

0

Mine Layers

5,000

2

0

2,000

0

2

Auxiliary Mine Layers

600

5

3

Torpedo Boats

600

12

8

Mine Sweepers

600

6

6

Emergency-net Layer

2,000

0

1

Net Tenders

600

0

2

Submarine Chasers

300

2

4

150

4

2

Repair Ship

10,000

1

0

Oil Tanker

17,000

1

0

Survey Ships

1,600

2

0

Submarine Tender

8,000

1

0

Collier

10,000

1

0

* Substitute for destroyer

--26--

Twenty-eight additional air units were to be reinforced under the plan for the replenishment of air strength.

In response to the foregoing, Navy Ministry authorities pushed the study of the recommendations. At the same time, they carried out negotiations with the Government. As a result, the Ministry sent the following answer on 15 November 1930:

Secretariat Secret Document No 1090

15 November 1930

From: Navy Minister ABO, Kiyotane

To: Chief of the Navy General Staff, TANIGUCHI, Naomi

Subject: Readjustment and Replenishment of Major Naval Strength

Upon presentation to the Prime Minister of a request of 7 October in regard to the subject mentioned in your Navy General Staff Secret Documents Nos 176 and 116, conferences were held by the executives of this Ministry and the general staffs. (See Appendix I) Due to the unfavorable state of national finances, the requests were slashed. Efforts were made, thereafter, to realize your proposals through repeated negotiations with the state ministers concerned.

As a result of these negotiations, a decision was reached at a Cabinet Meeting on the eleventh of this month. (See Appendix 2)

Incidentally, I will confer with the Prime Minister on the replenishment of armament not approved at this Cabinet Conference.

--27--

Appendix No. 1

Secretariat Secret Document No 943

7 October 1930

From: Navy Minister Baron ABO, Kiyotane

To: Prime Minister HAMAGUCHI, Yuko

Subject: Communication with reference to readjustment and Replenishment of Major Naval Strength

For various reasons not all of our recommendations were accepted at the London Naval Disarmament Conference. Therefore, it was anticipated that defects would appear in the forces which were to be used to carry out the naval operations program based upon the established national defense policy. This issue created a sensation across the length and breadth of the nation. Even in the Navy itself confusion arose over the issue and the situation was such that no one could foretell what the outcome would be. However, the fact that the situation appears to have settled outwardly is believed attributable to confidence felt in the sincerity of the government in naval rearmament matters.

I believe that the following are the principal causes contributing to the resolution of the issue.

When a Cabinet meeting was held on 1 April this year to discuss the instructions to be given to the Imperial Plenipotentiary, the Cabinet approved the Navy Vice-Minister's plan for easing difficulties expected in the strategic employment of forces for national defense as the result of the disarmament pact. Heated discussion ensued and

--23--

there appeared no end to the arguments during the unofficial meeting of the Supreme War Council held on 21 July to discuss whether the military strength authorized by treaty would hinder the strategic employment of forces for national defense, and the measures to be taken to correct the situation. On this occasion the Prime Minister, who had received situation reports from the ex-Minister of the Navy, declared that the government would, considering finances and other factors, make the utmost effort toward the realization of the rearmament program.

From this statement, the Supreme War Council understood the sincere attitude of the government and submitted a Reply to the Throne which was passed unanimously at the 23 July conference. The Prime Minister, shown the Reply by the Emperor, also replied to the Emperor, saying, "The reply of the Supreme War Council is just and right. I shall do my utmost to assist the Imperial Rule by carrying out the program, after careful deliberation with other cabinet ministers on the financial and other aspects of the program."

Needless to say, armament must be based upon national strength. Nevertheless, national defense is a matter which should be treated as a long-range policy of the nation, and at the same time the enhancement of national prestige and authority must be backed by powerful armament. For this reason, the greatest care should be exercised to see that the current financial hardships do not make one oblivious to the great necessity for rearmament. There is a danger that once rearmament is neglected, the day may come when a

--29--

regrettable situation could not be rectified. Considering the manner in which circumstances have developed to date, I firmly believe that from the standpoint of keeping the dignity of the government and exercising control over the Navy it is most imperative at this juncture to establish rearmament in line with the Reply to the Throne made by the Supreme War Council.

It is a cause of great anxiety to this minister that there are those who are apt to make light of rearmament, regarding the conclusion of the Disarmament Treaty as the advent of international peace. It is my belief that the United States will maintain a commanding position in the near future in naval armament. According to intelligence reports received to date, the program for auxiliary vessels proposed by the General Board, U. S. Navy, as shown in the appendix, aims at maximum buildup within limits of the treaty. In the case of capital ships, budgetary appropriations amounting to over 98,000,000 yen for remodeling ten dreadnoughts have already been approved by Congress, while the remaining capital ships are scheduled shortly to be modernized at the great cost of approximately 140,000,000 yen. Meanwhile, in the case of the air arm, U.S. Navy authorities are pressing for a goal of 1,000 aircraft as a second phase plan, in addition to the established program for the construction of 1,000 planes. From these facts one cannot help but conclude the disarmament treaty has not altered in the least the U. S. attitude toward naval rearmament.

Unless our country establishes and executes immediately a proper

--30--

naval armament replenishment program to cope with the situation, there is a likelihood that the gap in naval strength between Japan and the United States will widen increasingly, and our Just and rightful contentions will not be accepted, and we will fall prey to an overwhelmingly superior force. So far as our country is concerned, the maximum strength permitted under the treaty is inadequate from the standpoint of strategic employment of forces. We should try, therefore, to make most effective use of forces permitted by the treaty. Not only that, but the shortage of submarines and 8-inch cruisers should be rectified. At the same time, air strength should be reinforced in order to meet the requirements of national defense.

In line with the foregoing the Navy General Staff, after careful deliberation, mapped out the plan mentioned below and communicated it to the Navy Ministry. After several exchanges of opinion between the Navy General Staff and the Navy Ministry, it was agreed that the plan was right in principle.

I should like to add that the plan in question was presented as explanatory data on the occasion of the Supreme War Council's meeting to discuss measures to cope with the Naval Disarmament Treaty.

It is estimated that the implementation of this plan will cost as much as ¥ 733,633,000 in extraordinary expenditures alone. However, by reason of the points cited in the foregoing, it is desired that consideration be given to and every effort exerted for the realization of the plan, despite the fact that the implementation

--31--

of the plan in the present financial condition of the nation and financial policies pursued by the government is difficult.

Extract from the Naval Rearmament Program

The following plans are scheduled to be put into effect during the period from the 1931 fiscal year to the 1936 fiscal year:

Item

Necessary Expenditure

Shipbuilding & replacement program

¥ 422,983,000

Air strength reinforcement program

131,508,456

Various kinds of improvement programs

179,142,101

Total (Extraordinary expenditure)

¥ 733,633,557

Shipbuilding and Replacement Program

In view of the appearance of numerous superior warships of modern design in the United States, efforts must be directed toward minimizing the actual lowered effectiveness of the naval forces at the disposal of the Empire. Every possible effort must be made to build up forces to the limits prescribed by the treaty. At the same time, individual naval craft should be brought to maximum effectiveness. Meanwhile, replenishment of naval vessels not limited by treaty should be effected with a view to offset the difficulties imposed upon our strategic employment of forces by the treaty.

--32--

This program will be launched in the 1931 fiscal year and accomplished by 31 December 1936. The program concerning warships limited by treaty is to be accomplished by the end of the 1936 fiscal year. The construction of naval vessels limited by treaty to be under construction at the end of 1936 as well as those vessels not limited by treaty but which require construction during the period in question, is to be initiated in 1934 and completed by the end of the 1938 fiscal year.

--33--

SHIPBUILDING PROGRAM

Warships subject to the treaty limitations

Category of Warship

Standard Displacement

Unit Construction Cost

Number of Vessels to be Constructed and Construction Cost

Number of Vessels Scheduled to be started in 1934 and completed after 1937, and Construction Cost

Tons

¥

¥

¥

Cruisers

8,500

26,141,000

(4) 104,564,000

(2) 52,282,000

Aircraft carriers

9,800

29,000,000

(1) 29,000,000

0

Destroyers

1,400

5,750,000

(8) 103,500,000

(7) 40,250,000

Submarines

Large Cruising Ships

1,900

8,646,000

(1) 8,686,000

(2) 17,372,000

Navy Type Large Size

1,400

6,764,000

(6) 40,584,000

(2) 13,528,000

Medium Size

700

4,172,000

(2) 8,744,000

0

Total

Tonnage

Tons

Tons

Building

80,700

33,400

Cost

¥ 295,078,000

¥ 123,432,000

Warships not limited by treaty.

Coast-defense Ships

9,388,000

0

Large

900

2,217,000

4,435,000

0

Small

200

707,000

707,000

0

Mine Layers

5,000

7,650,000

15,300,000

0

2,000

4,709,700

0

9,419,400

Auxiliary Mine Layers

600

1,909,000

9,545,000

5,727,000

Torpedo boats

600

2,800,000

(12) 33,600,000

(8) 22,400,000

Mine Sweepers

600

1,880,000

11,280,000

(6) 11,280,000

Emergency Net layers

2,000

4,176,900

0

(1) 4,176,900

Net layers

600

1,798,000

0

(2) 3,596,000

Submarine Chaser, Large

300

1,600,000

(2) 3,200,000

(4) 6,400,000

Submarine Chaser, Small

150

1,131,000

(4) 4,524,000

(2) 2,262,000

--34--

Shipbuilding, Program

Warships not limited by treaty - Cont'd

Category of Warship

Standard Displacement

Unit Construction Cost

Number of Vessels to be Constructed and Construction Cost

Number of Vessels Scheduled to be started in 1934 and completed after 1937, and Construction Cost

Tons

¥

¥

Repair Ships

10,00

6,900,000

(1) 6,900,000

0

Oil Tanker

17,000

9,246,000

(1) 9,264,000

0

Collier

10,000

4,080,000

(1) 4,080,000

0

Submarine tender

8,000

10,500,000

(1) 10,500,000

0

Survey Ships

1,600

2,600,000

(2) 5,200,00

0

Total

Tonnage

Tons

Tons

78,000

18,900

Construction Cost

¥ 127,905,000

¥ 65,261,000

Grand

Total

Tonnage

Tons

Tons

159,000

52,300

Construction Cost

¥ 422,983,000

¥ 188,693,300

--35--

Of the amount shown in the foregoing table 422,983,000 yen represents the construction cost for the warships to be constructed by the end of the 1936 fiscal year. The construction cost of the warships to be constructed during the period between 1934 and the fiscal year of 1938 is omitted, according to the existing precedent of the continuing expenditure program.

The estimated expenditure by fiscal year is as follows:

Fiscal year

"

"

"

"

"

1931

1932

1933

1934

1935

1936

20,000,000

67,000,000

90,000,000

90,000,000

83,000,000

72,983,000

Total 422,983,000

In order to build the naval vessels allowed under the London Naval Treaty according to the standard ship age, the following average annual construction tonnage must be undertaken.

Category Auxiliary Ship

Tonnage permitted by Treaty

Ship Age for Replacement

Average Annual Tonnage Construction

8-in Cruisers

108,400 tons

20

5,420 tons

Light Cruisers

100,450 "

20

5,022 "

Destroyers

105,500 "

16

6,594 "

Submarines

52,700 "

13

4,054 "

Total

367,050 tons

21,091 tons

In addition to the above, there is need for the construction of

--36--

a large tonnage of replacement vessels in the categories of battleships, aircraft carriers and ships not restricted by treaty.

The number of the exempt ships to be constructed under the current program looms large compared with the annual construction of only 13,450 tons for auxiliary ships. Thus far, obsolete vessels have been used for defense and local operations, but since the London Treaty prohibits the possession of any vessel, even an obsolete vessel, in excess of limitations, it has become necessary to meet the depletion, as well as to construct new ships as replacements, so that normal peacetime duties may be carried out. The situation is such that it has become absolutely necessary to meet the shortage of submarines by use of certain vessels not limited by treaty. These points were taken into consideration when the program was formulated. To lower markedly our shipbuilding capacity and carry out a retrenchment of facilities and cut down personnel would not only bo difficult but would prove highly disadvantageous in the event that the necessity should arise in later years to revise shipbuilding at a moments' notice.

Air Strength Reinforcement Program

Air unite are to be increased by 16 units at a cost of 85,184,852 yen as a counter-measure to our limited naval strength, caused by the London Treaty.

Twelve air units at a cost of 46,323,604 yen are to be built, irrespective of the London Treaty, in view of the expansion of the US naval air force.

--37--

Various Plans for Replenishment

The following appropriations are considered necessary for vital programs and should be implemented at once and realized by the 1936 fiscal year:

Item

Amount

1.

Expenditure for improvement and modernization of warships and equipment, and incidental expenses

88,933,474 yen

2.

Expenditure for special ship repairs to prolong ship age and expenditure for ordnance repairs

33,560,000 yen

3.

Expenditure for replenishment of air force

9,502,194 yen

4.

Expenditure for increasing submarine force

6,125,500 yen

5.

Expenditure for equipment of research agencies

7,330,358 yen

6.

Increased expenditure for training and promotion of military effectiveness

6,690,575 yen

7.

Expenditure for improvement of defense facilities

27,000,000 yen

Total

179,142,101 yen

In addition to the foregoing, about 40,000,000 yen is being requested as running expenses, mainly for further training of personnel (air maintenance cost not included).

Should it prove impossible to realize Program No. 1 mentioned above by the 1936 fiscal year, it is desired that approval be given

--38--

to the implementation of the subscribed program, and that items of the original program be enforced successively as the financial situation improves.

The urgent program for the replenishment of the Navy. (Extract) It is planned that the following will be carried out during the period from the 1931 fiscal year to 1936 fiscal year.

Item

Necessary Expenses

Shipbuilding and replacement program

355,478,000 yen

Air strength reinforcement program

65,000,000 "

Various replenishment programs

80,000,000 "

Total (Extraordinary expenditure)

500,678,000 yen

--39--

Shipbuilding and replacement program

Category of warship

Standard
Displacement

Unit
construction
cost

No
of
ships
to
be
constructed.

Total
cost.

Warships
subject
to
the
treaty
limitation.

tons

yen

Cruisers

8,500

26,141,000

4

104,564,000 yen

Aircraft-carriers

9,800

29,000,000

1

29,000,000

Destroyers

1,400

5,750,000

18

103,500,000

Submarine-boats

Long cruising range type

1,900

4,444,000

1

4,444,000

Navy type large size

1,400

6,764,000

6

40,584,000

Medium size

700

4,372,000

2

8,744,000

Total

Tonnage:

80,700 tons

295,078,000 yen

Warships
on
the
exempt
list

Coast-defense ships

900

2,100,000

1

2,100,000

Gunboats

Large

900

2,000,000

1

2,000,000

Small

200

600,000

1

600,000

Minelayer

3,500

5,000,000

1

5,000,000

Minelayer

5,000

7,000,000

1

7,000,000

Light minelayers

600

1,700,000

5

8,500,000

Torpedo boats

600

2,600,000

8

20,800,000

Minesweepers

600

1,700,000

6

10,200,000

Submarine chasers (Small)

150

900,000

2

1,800,000

Survey ships

1,600

2,400,000

1

2,400,000

Total

Tonnage

23,400 tons

60,400,000 yen

Grand Total

Tonnage

104,500 tons

355,478,000 yen

Annual average for six years

Teenage

17,412 tons

59,246,000 yen

--40--

The estimated expenditure by fiscal year is as follows:

Fiscal year

"

"

"

"

"

1931

1932

1933

1934

1935

1936

yen 20,000,000

yen 75,000,000

yen 75,000,000

yen 75,000,000

yen 65,486,000

yen 44,992,000

Total 355,478,000 yen

Air strength replenishment program

The 16 units program: 65,000,000 yen.

Various replenishment programs

Expenditure: 80,200,000 yen

Appendix No. 2

Cabinet Decision Concerning Increase and Replenishment of Principal Naval Strength

11 November 1930

This program called for an expenditure of 424,000,000 yen, including 50,000,000 yen reserved for the construction and maintenance of two hew air units in and after the 1938 fiscal year. 247,080,000 yen was to be appropriated over six consecutive fiscal years from 1931 through 1936, for the construction of 39 naval vessels with a total tonnage of 75,300 tons, comprising 25 ships of those types placed under treaty limitations and 14 of those types outside the limitation.

The details are shown in the following table:

--41--

Urgent Program Increase and Replenishment of Principal Naval Strength

Classification

Expenditure

Remarks

Naval Vessels Construction and Replacement Program

247,080,000 yen

In addition 50,000,000 yen
appropriated for construction
of 2 air units, their maintenance, etc.

Air Strength Increase Program

81,970,000

Miscellaneous Replenishment Program

44,950,000

Total

374,000,000

50,000,000

For reference, the allocation of auxiliary naval vessels in total tonnage to Japan, Great Britain and the United States under the London Treaty is shown in the following comparison tables, (A) and (B), and the reply to the Throne made by naval members of the Supreme War Council upon the conclusion of said treaty is in (C).

--42--

(A) Comparative Table of Naval Craft Tonnage held by U. S. and Japan

Type of Vessel

Tonnage held by U.S.

Tonnage claimed by Japan

Tonnage limit under treaty

Difference
between claim
and treaty tonnage

Tonnage

Ratio (%)

Tonnage

Ratio (%)

Class-A Cruisers

180,000

126,000

70.00

108,400

60.22

17,600 ton

Class-B Cruisers

143,500

164,498

56.05

100,450

70.00

41,452

Destroyers

150,000

105,500

70.33

Submarines

52,700

77,842

Tonnage
considered
absolutely
necessary

52,700

100.00

25,142

Total

526,200

368,340

70.00

367,050

69.75

1,290

(B) Comparative Table of Naval Craft Tonnage held by Great Britain and Japan

Type of Vessel

Tonnage held by Britain

Tonnage claimed by Japan

Tonnage limit under treaty

Tonnage

Ratio (%)

Tonnage

Ratio (%)

Class-A Cruisers

146,800

126,000

85.83

108,400

73.84

Class-B Cruisers

192,200

164,498

48.07

100,450

52.26

Destroyers

150,000

105,500

70.33

Submarines

52,700

77,842

Tonnage
considered
absolutely
necessary

52,700

100.00

Total

541,700

368,340

68.00

367,050

67.75

--43--

(C) Reply to Throne adopted at meeting of the Supreme War Council concerning national defense in connection with Japanese naval strength as stipulated in London Treaty of 1930.

On 23 July 1930, a meeting of navy members of the councillors which was held in the Imperial Court, unanimously passed the following reply to the Throne: (Those present: Fleet-Admiral Togo, His Imperial Highness, Prince Fushimi, Councillor Okada, Councillor Kato, Minister, Chief of Navy General Staff, Chief of Operational Bureau, Chief of Military Affairs Bureau, Sumiyama, Aide to His Majesty.)

Reply to the Throne

The national defense policy sanctioned by Your Majesty in 1923 is the best policy to meet the present situation of the Empire. However, the recently concluded London Treaty creates a shortage in our naval strength required for the maintenance and execution of naval operation plans according to the established policy.

Accordingly, in order to minimize the effect of this shortage in strength after the treaty has gone into effect, the following measures must be taken by the end of 1936:

1. The full realization of the tonnage quotas stipulated in the treaty, improvement in the maintenance and of the potentiality of the existing naval vessels, and the increase of craft of those types which are outside the treaty limitation.

2. The expansion of air strength to an extent necessary for

--44--

the execution of the operation plan.

3. The improvement of defense installations, the strengthening of experimental and research organs, the improvement of training facilities, the encouragement of maneuvers and exercises, the increase of personnel and materials, the completion of land and sea installations, and the strengthening of preparations for tactical operations.

The enforcement of these measures is considered almost sufficient under the present situation to secure national defense, despite the restrictions imposed by the treaty. Nevertheless, since the disposition of the military forces of one nation should be determined according to the nation's own estimate of the situation in view of the nature of preparedness, we see it highly disadvantageous from the standpoint of national defense to remain for a long time under the restrictions imposed by this treaty. For this reason, we believe that the Empire should renew its efforts, upon the expiration of the treaty, for the completion of its defense setup with whatever policy is considered to be the best.

We submit this reply with the utmost reverence and humility.

23 July 1930

Signed by the Supreme War

Councillors

--45--

Appendix II

Navy General Staff Secret Document No 154

6 May 1933

From: Navy General Staff

To: The Navy Minister

Subject: Replenishment of Armament during and after the 1934 Fiscal Year

The international situation of the Empire has undergone unprecedented change since her withdrawal from the League of Nations, and the security of East Asia has come to depend entirely upon the actual power of the Empire.

Under these circumstances, the Japanese-American conflict of policies toward the Manchurian issue shows no sign of heading towards amicable settlement. Not only that but it appears that preparations for a solution by force of arms are being made in the United States. This is evidenced by the fact that her armament has steadily been increased since the Manchurian Incident and that her entire fleet has been concentrated on the Pacific coast, while air bases for use in time of war are being sought in central and southern China. Hereafter there may be some changes in the situation for better or for worse, but we must be prepared for the worst, as the general trend of affairs seems to be precipitating a crisis.

In view of the above-stated situation, it is deemed absolutely necessary that a national defense set-up strong enough to cope with

--47--

the crisis be created by supplementing, in the case of the Navy, the numerical inferiority of armament through the improvement of their quality, in addition to replenishment of air strength and warship construction during and after 1934 as envisaged in the communication, Navy General Staff Secret Document No 215 of 1932.

Your utmost efforts in the matter are hereby requested. (Postscript)

1. As to the construction of warships and the replenishment of air strength, it is expected that subsequent developments may require some modification of plans, at which time it is hoped to make further recommendations.

2. It is the intention of the Navy General Staff to have the Vice-Chief of the Navy General Staff confer with the Vice-Minister of the Navy on details of this communication.

Navy General Staff Secret Document No 199

14 June 1933

From: Chief of the Navy General Staff

To: Minister of the Navy

Subject: Construction and Replenishment of Naval Vessels and Replenishment of Air Strength

Navy General Staff Secret Document No 154 was forwarded to you previously with a view to coping with the general trends of future affairs. The steps which should be taken during and after 1934 in replenishment of armament were set forth in that communication. In view of steps now being taken by the United States to meet the new

--48--

situation in the Far East, especially in the light of their plans to push the replenishment of naval forces, it was deemed necessary to modify a section of plans outlined in Navy General Staff Secret Document No 215 of 1932. After careful deliberations, a plan envisaging the construction and replenishment of naval vessels as well as the augmenting of aerial forces, as given in the appended sheet, was formulated in order to effect adequate national defense and meet the international defense situation faced by our nation.

Your utmost efforts toward the realization of this plan are hereby requested.

--49--

Appendix to Navy General Staff Secret Document No 199

12 June 1933

From: Navy General Staff

Plan for Construction and Replenishment of Naval Vessels and Increase of Air Strength

1. In view of the Empire's international situation, brought about by the Manchurian Incident, and in anticipation of the various complications likely to arise during the forthcoming Disarmament Conference and subsequent to the expiration of the period of our notification of intention to withdraw from the League of Nations, there is a strong likelihood that Japan will face a still graver situation around 1935. Therefore, there is urgent need to replenish and equip the absolutely necessary forces to cope with the situation and provide adequate national defense.

However, the equipment of such forces, at this juncture, is impossible to accomplish immediately due to restrictions set forth in the London Treaty. Therefore, wherever possible, the execution of operations is to be facilitated by countering US naval rearmament by replenishing our forces within treaty limits, in accordance with the principles set forth in the Reply to the Throne made by the Supreme War Council at the time of the conclusion of the treaty in question.

Moreover, plans are to be formulated to see that our carrier-borne aircraft will not be inferior to those of the US Navy.

2. In the event that the US Navy's ship construction volume exceeds current expectations prior to the expiration of the London

--50--

Treaty, reinforcement of emergency air units is to be effected, while construction of vessels which are placed outside the limits is to be increased.

3. The plan is to be set into operation in the 1934 fiscal year and accomplished by the end of the 1936 fiscal year. However, the construction of one aircraft carrier and such types of vessels on which construction can be started, but which are not permitted under the treaty to be completed until the end of 1936, are scheduled to be completed at the end of the 1937 fiscal year.

Plan for Construction and Replenishment of Naval Vessels

Construction of naval vessels of restricted categories is to be carried out up to the limits prescribed by the treaty.

In the construction of naval vessels outside treaty limits, priority is to be given to the build-up of first line combat units, while in the case of defensive units, replenishment is to be made by employing, for the time being, obsolete vessels. At the same time forces are to be maintained at the minimum required strength in anticipation of an outbreak of hostilities.

Efforts are to be directed toward reinforcing cruising range and maneuverability of first line combat units.

--51--

SHIPS TO  BE CONSTRUCTED UNDER THE REPLENISHMENT PROGRAM

Ships Restricted by Treaty

Classification

Unit standard displacement Tonnage

Number of Ships

Maximum speed
(knots)

Cruising Range

Standard Armament

Description

Aircraft Carriers

10,050 tons

2

36

10,000 nautical miles at 10 knots

1. 20 mm guns 5 (equipped along center line)

2. 12.7 cm AA guns 20

3. Over 40 AA Machine guns

4. Aircraft (omitted)

1.  Internal combustion engines are to be used if possible.

2.  Number of planes that will be ready on the flight dock at any one time will consist of more than one half of the aircraft complement. Equipment will be so designed as to speed the take off and landing of the planes and also operation of the carrier. For this purpose, the number of planes in reserve may be decreased when necessary.

Cruiser Class-B

8,450 ton

2

10,000 nautical miles at 18 knots

1. 15.5 cm gun—triple mount 5 turrets

2. 12.7 cm AA guns—8

3. AA Machine guns—over 12

4. 61 cm Torpedoes—6 tubes mounts (broadside, upper deck)

5.  Catapults—4

6.  Aircraft-4

--52--

Ships to be Constructed under the Replenishment Program

(Ships Restricted by Treaty) - Cont'd

Classification

Unit standard displacement

Number of Ships

Maximum
speed

(knots)

Cruising Range

Standard Armament

Description

Destroyers

1,330 ton

14

over 36

4,500 nautical miles at 18 knots

1.  12.7 an guns—6

2. Over 4 AA Machine guns

3. 61 cm Torpedoes-8 tubes mounts

Submarines

1,900 ton

2

More than 21 on surface

14,000 nautical miles at 16 knots

1. 53 cm Torpedo tubes— 4 (bow)—2 (stern)

2. 12.7 cm AA guns—2

3. Anti-aircraft Machine guns more than 2

4. Catapult-1 Reconnaissance plane—1

1,400 tan

2

Over 23 surface

10,000 nautical miles at 16 knots

1.  53 on Torpedo tubes— 4 (bow)—2 (stern)

2. 10 cm AA guns more than 2

--53--

SHIPS NOT LIMITED BY TREATY

Classification

Unit
standard
displacement tonnage

Number
of ships
to be
constructed

Maximum
speed
(knots)

Cruising range
nautical miles

Description

Oil Tankers

10,000 ton

2

20

10,000 at 10 knots

Further Separate Communication

Seaplane Tender

9,000 "

3

20

8,000 at 16 knots

Torpedo Boats

600 "

16

34

3,000 at 6 knots

1. 12.7cm guns

4

2. AA Machine cans

more than 2

3. 61cm Torpedoes

4 tubes mounts

Submarine Chasers

300 "

20

1,500 at 14 knots

1. 40mm automatic cannon

2

2. Depth charges, depth-charge projector

(omitted)

150 "

12

20

i

500 at 14 knots

1. 40mm automatic cannon

1

2. Depth charges, depth-charge projector

(omitted)

Gunboats

1,000 "

2

20

more than
2,500 at 14 knots

1. 15cm guns

2

2. 15cm gen

1

3. AAMG

1

4. Internal-combustion engine used

200 "

1

18

over 1,500 at 14 knots

1. 15cm gun

1

2. AA Machine guns

more than 2

3. Internal-combustion engine used

Mine layers

5,000 "

1

20

5,000 at 14 knots

1. 15cm guns

4

2. Mines

omitted

3. AAMG

more than 4

--54--

Ships not limited by Treaty - Cont'd

Classification

Unit
standard
displacement

Number
of ships
to be
constructed

Maximum
speed

(knots)

Cruising
range
nautical
miles

Description

Repair ship

10,000 ton

1

10

8,000 at 14 knots

1. 12.7cm AA guns

4

2. AA Machine guns

more than 4

Emergency net
layer

2,000 "

1

20

2,000 at 14 snots

1. 12.7cm antiaircraft guns

3

2. Type 14 antisubmarine nets

(omitted)

3. AA Machine guns

as required

4. Depth-charge projectors

(omitted)

5. Depth-charges

as required

Coast-defense
ship

1,200 "

4

20

more than
5,000 at 14 knots

1. 12.7cm AA guns

4

2. AA Machine guns

as required

3. Depth-charge projectors

(omitted)

4. Depth-charges

as required

Minesweeper

600 "

6

more
than
20

3,000 at 14 knots

1. 12.7cm AA guns

3

2. AA Machine guns

as required

Survey ships

1,600 "

2

20

5,000 at 14 knots

1. 12.7cm AA guns

4

2. AA Machine guns

as required

Mine layer

2,000 "

1

20

3,000 at 14 knots

1. 12.7cm AA guns

3

2. Mines

(omitted)

3. Depth-charge

(omitted)

4. Dept-charge projectors

(omitted)

5. AA Machine gene

as required

Auxiliary
Mine
layer

450 "

5

more
than

20

1,500 at 14 knots

1. 40mm automatic cannon

2

2. Mine

(omitted)

3. Dept-charge projectors

(omitted)

4. Depth-charges

as required

--55--

Ships not Limited by Treaty - Cont'd

Classification

Unit
standard
displacement
tonnage

Number
of ships
to be
constructed

Maximum
speed

(knots)

Cruising
range
nautical
miles

Description

Net Tender

600 ton

2

20

1,500 at 14 knots

1. 40 mm automatic cannon

2

2. Nets

(omitted)

--56--

The plan for increasing air strength:

1. Purport

a. Aircraft carriers and plane-carrying ships (excluding escort carriers and converted vessels) are to be replenished so as to retain in peacetime all the crew which may be needed in wartime.

b. The replenishment and reinforcement of projected land-air groups is to be carried out so that air crew members will be available to man escort carriers, converted vessels and air groups (including specially established air groups) in the event of war.

c. Air reservists (including personnel in the first and second reserves) are to be replenished in addition to the rapid training of air crew members, should the occasion require, as no time is to be lost in augmenting the shortage of the crew which we might need in wartime.

2. (omitted)

3. Land air groups

(First part omitted)

a. Nine understrength units among the existing air groups are to be reorganized.

b. Among the projected groups, 3 1/2 groups are scheduled for completion in the 1936 fiscal year.

c. Eight new groups are to be established.

d. The 21 existing groups, 10 projected groups, and eight groups to be reinforced, are to be equipped by the 1936 fiscal year.

4. Air reservists (including those in the first and second

--57--

reserves) who are subject to call in wartime and are capable of assuming various air duties after supplementary training of less than five months, are to be assigned to units cited in paragraph c, above

--58--

APPENDIX III

OUTLINE OF SECOND NAVAL REPLENISHMENT PLAN

Category

Number of Vessels

Tonnage per Vessel

Total Tonnage

Class of Warship

Keel Laid

Completed

Aircraft carrier

2

10,050

20,100

Hiryu Class

Nov 1934

Jul 1939

Light cruiser

2

8,500

17,000

Tone Class

Dec 1934

hay 1939

Destroyer

14

1,368 (4)

20,472

Shiratsuyu Class (4)

May 1935

Jun 1939

(Usikaze and others)

1,500 (10)

Asashio Class (10)

Submarine

4

1,950 (2)

6,700

Large Cruising Type (2)

1,400 (2)

Navy Type Large size (2)

Sep 1934

Dec 1938

Seaplane tender

3

9,000

Chitose Class and Mizuho

Nov 1934

Feb 1939

Submarine tender

2

12,000

24,000

Tsurugizaki Class (Takasaki
was converted into an aircraft
carrier in the course of building)
Originally designed as tankers
(9,500 x 2 - 19,000) converted into
submarine tenders on 15 Sep 38

Jan 1938

Dec 1940 (Aircraft carriers)

Torpedo boat

16

595

9,520

Otori Class (8)

Nov 1934

Sep 1937

Cancelled (8)

Submarine chaser

4

270 (1)

780

No. 1 Class (1)

Apr 1935

Jul 1939

170 (3)

No. 51 Class (3)

--59--

Outline of Second Naval Replenishment Plan - Cont'd

Category

Number of Vessels

Tonnage per Vessel

Total

Class of Warship

Keel Laid

Completed

Repair ship

1

9,000

9,000

Akashi

Jan 1937

Total

48

134,572

A four-year program with a budget of 431,688,000 yen was approved.

--60--

Appendix IV

Disposition of Air Units After Completion of Plan 2 - End of 1936

Program

Old Program (17 units)

Program NO. 1 (14 units)

Program No. 2 (8 units)

Grand Total

Number of units after Reorganization

Description

Location

Type of Aircraft

Yokosuka

Tateyama

Kasumigaura

Sasebo

Omura

Ominato

Konoya

Meizuru

Chinkoi

Total

Yokosuka

Tateyama

Kasumigaura

Yokohama

Chinato

Kure

Sasebo

Omura

[entire column unreadable]

Total

Yokosuka

Yokohama

[]

Chinato

Saeki

Omura

Kanoya

Total

Land Trainer

1/2

2 1/2

3

3

3

Reorganized and strengthened from 2 carrier-born reconnaissance plane units, 1/2 carrier-borne units, 1/2 carrier-borne attack plane [ ] unit & 1/2 small size flying boat unit.

Sea
trainer

1/2

2 1/2

3

3

3

Carrier-borne fighter

1/2

1/2

1

2

1/2

1/2

1/2

2

1/2

1/2

1/2

1

2 1/2

6 1/2

6 1/2

Carrier-borne bomber

1/2

1/2

1 1/2

1/2

2

2

Carrier-borne
attack plane

1

1

1 1/2

1

1/2

1/2

5

5

Medium-size attack plane

1

1/2

1/2

1/2

2 1/2

1/2

(1/2)

(1/2)

(1)

1/2 (2)

3 (2)

5

Reorganized and added from 1 1/2 small-size flying boat units.

Large-size
attack
plane

1 (1)

1/2 (1)

1/2 (1)

1 1/2

Reconnaissance
seaplane

1/2

1/2

1

1/2

1/2

1/2

4

1

1/2

1/2

[ ]

6

6

Small-size flying boat

1/2

1/2

1/2

1/2

1 1/2 units reorganized into medium-size attack plane units.

Medium-size flying boat

1

1

[ ]

3

3

Large-size flying boat

1

1

(1)

(1)

1 (1)

2

"Research"

1/2

1/2

1

1/2

1/2

1 1/2

Total

3

2

6 1/2

1

2 1/2

1/2

1/2

1/2

1/2

17

3 1/2

3

1

1

1/2

1

1

1/2

[ ]

1/2

(1)

1

(1)

1/2 (1/2)

1/2

1/2 (1/2)

1

(1)

4

(4)

35

(4)

39

Note

1. 1/2 reconnaissance seaplane units each for Matsura and Chinoki [in] Old Program column was changed in Program No. 2 to 1/2 reconnaissance seaplane unit for Tatoyam and Kure.

2. 1/2 medium-size attack plane each for Omura, Ominate and Kanoya [in] Old Program column was changed from 1/2 small-size flying boat unit for Sasebo, Tateyama and Saoki after reorganization.

3. Numbers of units in parenthesis in Program No. 2 column indicated units not yet organized as of end of fiscal year 1936.

Navy Aeronautical Department, General Affairs Bureau, 2nd Section

1 September 1936

 

Japanese Monograph No. 149

OUTLINE OF NAVAL ARMAMENT AND PREPARATIONS FOR WAR

Part II

PREPARED BY MILITARY HISTORY SECTION HEADQUARTERS, ARMY FORCES FAR EAST

DISTRIBUTED BY OFFICE OF THE CHIEF OF MILITARY HISTORY DEPARTMENT OF THE ARMY

FOREWORD

This is the second of a series of six monographs in regard to Japan's naval armament in preparation for and during the Pacific War.

Additional monographs covering Japan's naval armament plans are:

Mono No

Outline of Naval Armament and Preparations for War, Part I

145

Outline of Naval Armament and Preparations for War, Part III

160

Outline of Naval Armament and Preparations for War, Part IV

169

Outline of Naval Armament and Preparations for War, Part V

172

Outline of Naval Armament and Preparations for War, Part VI

174

--iii--

Preface

Through Instructions No. 126 to the Japanese Government, 12 October 1945, subject: Institution for War Records Investigation, steps were initiated to exploit military historical records and official reports of the Japanese War Ministry and Japanese General Staff. Upon dissolution of the War Ministry and the Japanese General Staff, and the transfer of their former functions to the Demobilization Bureau, research and compilation continued and developed into a series of historical monographs.

The paucity of original orders, plans and unit journals, which are normally essential in the preparations of this type of record, most of which were lost or destroyed during field operations or bombing raids rendered the task of compilation most difficult) particularly distressing has been the complete lack of official strength reports, normal in AG or G3 records. However, while many of the important orders, plans and estimates have been reconstructed from memory and therefore are not textually identical with the originals, they are believed to be generally accurate and reliable.

Under the supervision of the Demobilization Bureau, the basic material contained in this monograph was compiled and written in Japanese by former officers, on duty in command and staff units within major units during the period of operations. Translation was effected through the facilities of Allied Translators and Interpreters Service, G2, General Headquarters, Far East Command.

This Japanese Operational Monograph was rewritten in English by the Japanese Research Division, Military History Section, General Headquarters, Far East Command and is based on the translation of the Japanese original. Editorial corrections were limited to those necessary for coherence and accuracy.

--v--

TABLE OF CONTENTS

Page

Chapter I

The Third Replenishment Plan

1

The Plan and Subsidiary Means Used to Replenish Naval Surface Strength

2

Air Strength Plan

7

Chapter II

Acceleration of War Preparations and Supplementary Armament Plans Caused by Outbreak of China Incident

11

Acceleration of War Preparations

11

Supplementary Armament Plan

14

Extraordinary Military Expenditure

16

The Fourth Replenishment Plan

17

Appendix I

Third Replenishment Plan

25

Ship Construction

25

Aircraft Preparation - Land-based

27

Aircraft Preparation - Land-based Air Group

27

Appendix II

Expected Air Strength at the Time of the Completion of the Third Replenishment Plan

29

Appendix III

Outline of the First War Preparations Analysis Conference

31

Appendix IV

Fourth Replenishment Plan of the Naval

34

Aircraft Preparation - Land-based Air Group

34

Shipboard Air Strength

35

Ship Construction

37

--vii--

TABLE OF CONTENTS (CONT'D)

Page

Chart No. 1

Approved Budget (Fiscal year 1937)

3

Chart No. 2

Ship Construction Progress of Third

6

Chart No. 3

Budget (Fiscal year 1939)

20

Chart No. 4

Ship Construction Progress of the Fourth

21

--viii--

Chapter I The Third Replenishment Plan

In December 1934, Japan submitted notification of the abrogation of the Washington Treaty. At the same time, after intensive research for the coming disarmament conference, it was found that Japan did not have the facilities, material or money to compete with the western powers in naval armament. It was planned, therefore, that in order to safeguard herself, Japan would stress the point of finding the common upper limit of naval strength and of reducing or entirely abolishing offensive vessels, such as battleships and aircraft carriers. It was felt that the naval ratio that had been adopted both in the Washington and London Treaties was unreasonable and would not guarantee the security of Japan.

The Naval Disarmament Conference of the five powers, Japan, Great Britain, United States, France and Italy was held in London in December 1935. Since Great Britain and the United States not only disagreed in principle with Japan's contention that the naval treaty was unreasonable, but ignored it, Japan withdrew from the conference in January 1936. Thus, with the expiration of both the Washington and First London Naval treaties, Japan was no longer committed to any treaty obligations with Britain and the United States.

These events combined to make Japan feel herself in an isolated position in regard to the Occidental powers. In addition, from the time of the establishment of Manchukuo the Chinese people had openly

--1--

shown their resentment against Japan, and, especially in North China, armed clashes were frequent. With the marked increase of clashes in Asia between Japan and China and between Japan and the Soviet Union, Japan began to feel pressure from all sides, which she believed would have to be overcome at any cost.

In March 1936, Great Britain requested the Japanese Government to take part in the limitation of guns on capital ships provided in the Second London Naval Treaty (British-American-French Naval Qualitative Limitations Treaty) but Japan declined the invitation. Since the end of 1935, in view of the unexpected delay in carrying out the Second Naval Replenishment Plan, Japanese naval authorities had been preparing for the next armament replenishment plan. As a result, the Third Replenishment Plan, extending over five years (four years in the case of aircraft) beginning in the 1937 fiscal year, was formulated. This plan called for a total of 66 ships (including two battleships) amounting to approximately 270,000 tons; also included in the plan were 14 new air units, bringing Japan's total air strength to 53 units. (See Appendix I) The approved budget for shipbuilding was approximately 800,000,000 yen. (3 1/2 yen = $1.00) (See Chart I) The progress of ship construction is shown in Chart 2.

The Plan and Subsidiary Means Used to Replenish Naval Surface Strength

This was the first plan made and put into effect by the Japanese Navy after it had been freed from obligations of international dis-

--2--

Chart — 1 Approved Budget (Fiscal year 1937)

Type of Ship

Tonnage

Number of Ships

Cost (in 1,000 yen)

Total (in 1,000 yen)

Battleships

35,000

2

98,000

196,000

Aircraft Carriers

24,500

2

80,850

161,700

Minelayer (Class A)

11,600

1

24,940

24,940

Minelayer (Class B)

5,400

1

9,750

9,750

Emergency Net Layers

2,000

2

4,500

9,000

Escort Ships

1,200

4

3,060

12,240

Gunboats (Class A)

1,000

2

3,300

6,600

Gunboats (Class B)

270

2

1,174.5

2,349

Destroyers

2,000

18

9,000

162,000

Submarines (Class A)

2,600

2

14,560

29,120

Submarines (Class B)

2,100

12

12,180

146,160

Minesweepers

600

6

2,130

12,780

Naval Transport

10,000

1

4,400

4,400

Survey Ship

1,600

1

3,760

3,760

Light Minelayers

700

5

2,450

12,250

Subchasers

300

9

2,450

13,500

Total

70

806,549

Budget Appropriation for Each Fiscal Year (in 1,000 yen)

Total

1937

1938

1939

1940

1941

806,549

48,007

206,342

232,392

229,057

90,751

In addition, on account of a rise in prices, a 57,669,038 yen increase was authorized for the fiscal year 1941.

--3--

armament treaties. Every effort was to be made to compensate for lack of quantity in naval strength by the improvement of quality. To do this, it was necessary to re-equip vessels in order to make each ship as effective as possible.

Battleships

Due to lack of facilities, materials and the time necessary for construction. and from the viewpoint of expense, it was realized that it would be impossible to raise the ratio of battleships. Therefore, as the Japanese Navy could not compete with the United States Navy in regard to the number of battleships, it was decided to construct the two largest and most effective battleships in the world, the Yamato and Musashi.

Since 1931, with each armament plan, the modernization of capital ships had been carried out. The conversion of the nominal training ship Hiei back to a battleship was begun in 1937, when the ship was freed from treaty limitations.

Aircraft Carriers

In view of the vulnerability of aircraft carriers, quantity rather than quality of carriers was given first consideration, and a policy was adopted whereby the ratio of Japanese aircraft carriers would be kept equal to, if not greater than, that of the United States.

It was considered that the two aircraft carriers of the Shokaku class, which had been included in the Third Replenishment Plan (See

--4--

Chart 2) would easily be able to balance the United States Navy in the number of carriers completed in accordance with the First Vinson Plan. However, since 1937 the United States had been planning an increase in aircraft carriers. It was also reported that the number of carriers to be constructed according to the Second and Third Vinson Plans would total between 8 and 10. It seemed therefore that, in spite of the Japanese plan to maintain parity with the United States, this would not be realised. Under the circumstances the Japanese Navy decided to conduct intensive research and investigation into the progress of the United States naval armament, and, if necessary, in order to obtain parity, to requisition and convert first-class merchant ships into aircraft carriers.

Cruisers

The Japanese Navy's most favorable ratio with the United States Navy, under treaty restrictions, was cruisers. Generally speaking, however, the number of Japanese cruisers could not exceed 70 percent of the United States cruisers. The Japanese Navy, therefore, adopted a policy of equipping each cruiser with as many guns and torpedoes as possible. Furthermore, with the removal of treaty restrictions, it was able by the end of the 1938 fiscal year to complete the Conversion of the light cruisers Mogami and Mikuma into heavy cruisers, by replacing 155mm guns with 200mm guns.

The light cruisers Kumamo and Suzuya, which were of the same type as the Mogami, and the Tone and Chikuma, which were based on the

--5--

Chart-2 Ship Construction Progress of Third Naval Replenishment Plan

Type

Period of Construction

Ships

Battleships

Nov 37 to Aug 42

Yamato Musashi

Carriers

Dec 37 to Sep 41

Shokaku Zuikaku

Seaplane tender

Nov 38 to Jan 42

Nisshin

Minelayer

Jul 39 to Oct 41

Tsugaru

Emergency Netlayer

Apr 38 to Jun 40

Hatsutake Aotaka

Escort Ships

Hot 38 to Mar 40

4 - Shimsihu Class

Gunboats (Class A)

Feb 39 to Apr 41

Hashidate Uji

Gunboats (Class B)

Aug 38 to May 40

Fushimi Sumida

Destroyers

Sap 37 to Jun 41

15 - Kagero Class

Submarines (Class A)

Jan 38 to Oct 41

1 - I-9 Class 1 - I-10 Class

Submarines (Class B)

Jan 38 to Oct 41

6 - I-15 Class

Submarines (Class C)

Aug 37 to Oct 41

5 - I-16 Class

Subchasers

Oct 37 to Aug 39

6 - No. 7 Class

Naval transports

Jul 39 to Jul 40

Kashino

Survey ship

Jan 40 to Jan 42

Tsukushi

Light Minelayer

Jun 37 to Oct 40

5 - Sokuten Class

Minesweepers

Oct 37 to Jun 39

9 - No. 4 Class

TOTAL: 66 ships, approximately 277,000 toss.

(Note) Construction of three destroyers and one submarine was cancelled in order to divert the funds to the construction of the two super-battleships, Musashi and Yamato

--6--

Second Replenishment Plan, were in the process of construction, so that they could be completed as heavy cruisers, without going through the process of conversion.

Thus, when the Second Replenishment Plan was fully carried out, the number of heavy cruisers in the Japanese Navy totalled eighteen. In spite of the fact that the Third Replenishment Plan did not include the construction of cruisers, it appeared that, as far as cruisers were concerned, the Japanese Navy would be able to maintain an almost equal strength with the United States Navy.

Air Strength Plan

Although the budget appropriation approved for the preparation of air strength of approximately 140,000,000 yen, reaching a total of about 200,000,000 yen by the addition of various other subsidiary expenditures, may appear small when compared with the 800,000,000 yen for shipbuilding scheduled in the Third Replenishment Plan, this was actually not so. The expenditure for the maintenance and replacement of 53 land-based air units and about 600 shipboard aircraft, when this plan was carried into effect, totalled an extraordinarily large amount. Moreover, with the rapid increase in air strength, airfields had to be constructed and expanded. Factories also were established under the administration of the Naval Aeronautical Department for the manufacture, maintenance and repair of aircraft equipment.

--7--

With the commencement of the Third Replenishment Plan, not only did the Naval Aeronautical Department become more and more important as a training control unit, but its duties as a repair and construction control organ brought it more closely in line with the Naval Technical Department. This situation resulted in subsequent approved budgets being almost equal for both organs.

Soon after the commencement of the Third Replenishment Plan, the China Incident broke out, so that the operational loss of naval aircraft showed a rapid increase, with the resultant difficulties in executing armament plans and activating forces. Measures were taken at this time to obtain unanimous approval of the Extraordinary Military Expenditure (See p. 16). Increase of industrial production was intensified with the expansion of the war front, and, in spite of the fact that it became necessary to increase various emergency armament and war preparations for the China Incident, their completion was successfully expedited. The bulk of the land-based air force (totalling 12 units excluding one unit of medium attack planes and one unit of medium flying boats) was completed by the end of the fiscal year 1938; the uncompleted unit of medium attack planes was completed within the fiscal year 1939 and the medium flying boats within the fiscal year 1940. The completion of shipboard strength was realised between 1938 and 1941 (except for aircraft for the Musashi which was completed in 1942) according to the time of completion of shipbuilding.

--8--

The grand total of air strength at the time of the completion of this plan was roughly estimated as shown in "Expected Air Strength at the Time of Completion of the Third Replenishment Plan" (See Appendix II) though it was subject to many additions and changes with the development of the China Incident.

The preparation of land air bases steadily progressed with the preparation of aircraft. Land-based air groups which were activated by the end of 1940 were as follows:

Name of Air Group

Date of Activation

Note

1

YOKOSUKA

1 Apr 1916

According to the Second Replenishment Plan

2

SASEBO

1 Apr 1918

3

KASUMIGAURA

1 Nov 1922

4

OMURA

1 Nov 1922

5

TATEYAMA

1 Jun 1930

6

KURE

1 Jun 1931

7

OMINATO

1 Nov 1933

8

SAEKI

5 Feb 1934

According to the Second Replenishment Plan

9

MAIZURU

1 Oct 1935

10

KISARAZU

1 Apr 1936

11

KANOYA

1 Apr 1936

12

CHINKAI

1 Oct 1936

13

YOKOHAMA

1 Oct 1936

--9--

14

TAKAO

1 Apr 1938

According to the Third Replenishment Plan

15

SUZUKA

1 Apr 1938

16

OITA

5 Dec 1938

17

TSUKUBA

5 Dec 1938

18

KASHIMA

5 Dec 1938

19

CHICHI JIMA

1 Apr 1939

20

USA

1 Oct 1939

21

CHITOSE

1 Oct 1939

22

YATABE

1 Deo 1939

23

HYAKURIHARA

1 Dec 1939

24

IWAKUNI

1 Dec 1939

25

TSUCHIURA

5 Nov 1940

26

MIHORO

1 Oct 1940

According to the

Fourth Replenishment Plan

27

GENZAN

1 Oct 1940

28

TOKO

1 Oct 1940

29

HAKATA

5 Not 1940

--10--

CHAPTER II

Acceleration of War Preparations and Supplementary Armament Plans Caused by Outbreak of China Incident

Acceleration of War Preparations: At the time of the outbreak of the China Incident in July 1937, the Third Replenishment Plan was already under way, and the subsidiary preparations to modernise existing ships and reorganize air groups were making steady progress. In order to prevent obstructing the execution of the armament program, the Japanese Government and the Navy desired to localise the Incident. However, the Incident spread to Central and South China, causing a general clash between Japan and China.

In early and middle July the Navy made preparations to cope with the situation (See Monograph No. 144; "Political Strategy prior to Outbreak of War," Part I, 1931-1939, Chapter II.) These preparations included:

a. Reorganisation of units and deployment of necessary strength for emergency to include the activation, preparations for deployment and alerting of two Special Combined Air Groups and a Special Naval Landing Force.

b. Drafting of necessary personnel.

c. Acceleration of manufacturing and stockpiling of equipment, war materials (especially materials impossible to import in wartime), bombs and machine gun ammunition.

--11--

d. Preparation for requisitioning necessary ships and complete equipment of navy vessels.

e. Establishment of necessary facilities for defense of key positions.

By the middle of August, the main results obtained from the above preparations were:

a. The Aoba and Kinugasa, having been repaired, were engaged in army transportation as guard ships.

b. The Belfast Maru, Kinugasa Maru and Choko Maru had been requisitioned.

c. The Asahi Maru had been requisitioned and converted into a hospital ship, while a special sick bay had been organized aboard the hospital ship Muroto.

d. The First Naval Harbor Master's Department had been established aboard the naval auxiliary ship Asahi, and this ship attached to the Third Fleet and used for salvage and repair.

e. The necessary facilities for the transportation of a Special Naval Landing Force to the Tsingtao area had been installed on the Settsu and Yakaze.

On 13 August 1937, the Chinese Army made an attack on a Japanese naval land combat unit at Shanghai, which precipitated the two armies into a full-scale war.

Believing that the Incident would continue to expand for a considerable time, and that friction with the Three Powers would necessarily increase during that period, the Navy determined to

--12--

accelerate war preparations immediately to cope with the situation. On 23 August, in order that the Chief of Navy General Staff might present his views to the Navy Minister, the First War Preparations Analysis Conference was held. (See Appendix III)

In spite of the capture of Nanking in November 1937, the China Incident dragged on, and cases of protest and interference by the Three Powers occurred so frequently that the execution of war preparations based on the conferences held on all such occasions between the Navy Ministry and the Navy General Staff became standard procedure. Moreover, preparations covering a long period were to be given priorities by weighing their importance with the existing and next armament plans, and by advancing their completion dates in the form of additional armament. Special emphasis was placed on:

Replenishment of aircraft lost in operations

Obtaining and training aircraft personnel

Completion of operational air bases and strengthening of their defenses

Gradual overhaul or modernization of all existing navy vessels

Gradual requisitioning and conversion of ships and construction of miscellaneous small ships

Procurement, increased production, storage and supply of required war materials

Strengthening of various land and sea facilities along with the completion of the above strength and equipment.

--13--

Supplementary Armament Plan

In order to achieve the objectives agreed upon by the Navy Ministry and the Navy General Staff, it became obvious that it would be necessary to execute an additional armament plan for the period between the Third and Fourth Replenishment Plans.

Ship Strength

In the fiscal year 1938, a budget appropriation of 17,200,000 yen for the construction of three ships — two training ships (three requested) and one storeship (two requested) — was approved as an expenditure extending to 1941. The construction of these ships was to be carried cut together with the Third Replenishment Plan.

The obsolete ships used for training had always been regarded as a disgrace and, with the sharp increase in the number of cadets, and the tremendous development in ships' equipment and tactics, it became absolutely necessary to replace them. The Katori and Kashima (displacement tonnage per ship 5,800 tons) were completed and commissioned as training ships in April and May 1940 respectively.

One storeship, the Irako (displacement tonnage, 9,570 tons) was completed and commissioned in December 1941. However, with the expansion of the area of fleet training and the extension of the training period, this one storeship was considered completely inadequate to cope with the situation.

--14--

Air Strength

The Navy General Staff requested 75 additional medium attack planes for the war with China within the fiscal year 1937. This meant almost doubling the existing strength of medium attack planes within half a year. Every effort was made to accelerate production by advancing to the utmost the date of completion of two and a half units of medium attack planes in accordance with the Third Replenishment Plan, completing three units of medium attack planes as an additional armament plan in 1938, and reinforcing the Kanoya and Takao Air Groups with the above units, thus expediting the replenishment of loss by the operational forces.

It required great effort to replenish and maintain air strength even in peacetime. It was, therefore, found extremely difficult to maintain combat strength by the prompt replenishment of losses in the China operations, and, at the same time, to plan the increase in strength demanded by the armament plan, For instance, the number of aircraft which was scheduled to be completed by the third year of the China Incident as a replenishment, or strengthening, of war preparations for the Incident, in addition to aircraft scheduled in the existing armament plan (excluding the above mentioned additional armament of three units of medium attack planes) was estimated as shown below:

--15--

Carrier Fighters

131

Carrier Bombers

57

Carrier Attack Planes

71

Reconnaissance Seaplanes

59

Medium Attack Planes

72

Heavy Attack Planes

0

Transports

0

Total

390

Needless to say, these figures indicated the budgetary strength which was estimated after considering the Extraordinary Military Expenditure appropriation, not the actual strength which was assigned and committed to the China operations. It is interesting to note that the actual number of aircraft completed in a year was much the same as the total number of aircraft scheduled in past armament plans covering several years.

Extraordinary Military Expenditure

With the outbreak of the China Incident, measures were taken to obtain unanimous approval of the Extraordinary Military Expenditure. This was done not only from the standpoint of urgency of operations and preservation of secrets, but it was also a very effective means of accelerating armament and war preparations.

In the past the expenditure of the budget had been restricted within narrow limits. The Extraordinary Military Expenditure made lt possible to divert money from one item or expenditure to

--16--

another or to expend it for a new item in accordance with changes in plans.

The Fourth Replenishment Plan

Soon after the outbreak of the China Incident, the Chinese Government submitted a protest to the League of Nations. The United States Government in October 1937, as though in concert with this action accused Japan of violating the Kellogg Pact. Anti-Japanese feeling in both Great Britain and the United States was aggravated at this time by the Panay and Lady Bird Incidents, caused in connection with the capture of Nanking. Although these incidents, themselves, were settled by diplomatic measures, with the expansion of operations in Central and South China, cases of violations of rights and interests, particularly of Great Britain and the United States, occurred so frequently that anti-Japanese feeling became increasingly evident. This, together with the acute situation in Europe, caused both Great Britain and the United States to greatly accelerate the strengthening of armament and war preparations.

The German-Austrian Anschluss and the German invasion and annexation of the Sudeten area, which were carried out in the spring and fall of 1938, seemed to be drawing Europe closer to a great cataclysm. World conditions caused Great Britain and France to place themselves on a quasi-wartime footing, and the United States to further step up armament and war preparations against the Axis Powers.

--17--

The armament of the United States Navy, according to the First Vinson Plan for the fiscal year 1934, was to be expanded to the limit permitted by the treaty. Moreover, a budget for an increase of 2 battleships, 20 destroyers, 6 submarines and 333 aircraft was approved in 1936. In addition, a plan for a huge amount of armament, totalling 81 vessels, was announced for the fiscal year 1937: 2 battleships, 3 aircraft carriers, 11 cruisers, 16 submarines, 48 destroyers and 1 gunboat. Besides this, a budget for the construction of two replacement battleships from the fiscal year 1939 onward was requested. Furthermore, in May 1938, the Second Vinson Plan, requiring 46 combat ships (including three battleships and two aircraft carriers), 26 auxiliary ships, 950 aircraft and one airship was signed by the President. The Second Vinson Plan was a ten-year plan. At the same time, a budget for about 1,100,000,000 dollars was passed for land and sea facilities.

In view of the United States increase in strength according to the plan for the fiscal year 1937, and the Second Vinson Plan, which was approximately four times that of the Third Replenishment Plan for the Japanese Navy, Japan, in spite of her difficulties in China, felt forced to cope with the situation at any cost by means of another armament plan.

The Japanese Navy was confronted with the absolute necessity of completing its armament, while on the other hand, operations on

--18--

the Chine mainland necessarily required priority of Army armament. This gave rise to a number of problems in regard to the financial and material limits of the country. In the meantime, the Navy Ministry and the Navy General Staff, upon investigating the contents of the two huge armament plans of the United States Navy, advanced the next armament plan, aiming at Japan's ship strength to at least equal one of the American plans, and her air strength to be on parity. They continued negotiations with the ministries concerned until at last in 1939 the budget passed the Diet. This was known as the Fourth Replenishment Plan of the Naval Armament Completion Plan for the fiscal year 1939. (See Appendix IV) An approved budget of approximately 1,200,000,000 yen was appropriated for the construction of 83 vessels (including two battleships). (See Chart 3) The progress of construction of these vessels is shown in Chart 4. In air strength, this plan called for 75 units as a nucleus comprising 34 1/2 operational units and 40 1/2 training units, both of which belonged to land-based air forces. About 300,000,000 yen was appropriated solely for the construction of aircraft. This plan was intended to cover six years (five years in the case of air strength) from the fiscal year 1939 to 1944.

The Third Naval Replenishment Plan aimed to double the naval air strength in five years, in spite of the fact that it had taken over 20 years to build it to its present strength. The Navy did

--19--

Chart — 3 Budget (Fiscal year 1939)

Type

Tonnage

Number

Cost (in 1,000 yen)

Total Cost (in 1,000 yen)

Battleships

40,000

2

130,000

260,000

Carrier

28,500

1

101,175

101,175

Cruisers (Class B)

6,600

4

26,400

105,600

Cruisers (Class C)

8,200

2

31,160

62,320

Destroyers (Class A)

2,100

18

10,605

190,890

Destroyers (Class B)

2,600

6

12,090

72,540

Cruising Submarines (Class A)

2,600

1

16,640

16,640

Cruising Submarines (Class B)

2,200

15

14,190

212,850

Submarines (Navy Large Type)

1,600

10

10,480

104,800

Training Ship

6,000

1

7,200

7,200

Seaplane tender

5,500

1

11,825

11,825

Light Minelayers

700

10

2,660

26,600

Mine sweepers

700

6

2,660

15,960

Subchasers

300

4

1,620

6,480

Emergency net layer

2,000

1

4,900

4,900

Oil tanker

5,000

1

6,000

6,000

Total

83

1,205,780

Annual Budgets (in 1,000 yen)

1939

1940

1941

1942

1943

1944

Total

60,150

119,250

289,785

384,184

290,080

62,330

1,205,780

These budgets were approved as general accounts. However, they were included in the extraordinary military expenditure after the fiscal year 1942.

--20--

Battleship 110

Apr 40 to Dec 40

Construction in progress

Dec 40 to Jun 42

Construction suspended

Jun 42 to Nov 44

Converted to carrier Shinano

Battleship 111

Nov 40 to Dec 40

Construction in progress

Dec 40 to Mar 43

Construction suspended

Mar 43

Dismantled

Carrier

Jul 41 to Mar 44

Taiho

Cruiser (Class B)

Jun 40 to Nov 44

4 Agano Class cruisers

Cruisers (Class C)

1939

1 ship - construction suspended.

Feb 41 to Feb 43

Oyodo

Destroyers (Class A)

May 39 to Jul 43

3 Kagero Class

12 Yugumo Class

1 Shimakaze

Destroyers (Class B)

Jul 40 to May 43

6 Akitsuki Class

Submarine (Class A)

Apr 40 to May 42

I-11 Class Submarine

Submarine (Class B)

Jun 39 to Apr 43

I-14 I-15 Class Submarines

Submarine (Navy Large Type)

Jun 40 to Aug 43

10 I-176 Class submarines

Training ship

Oct 39 to Jul 41

Kashii

Seaplane tender

Nov 40 to Apr 42

Akitsushima

Light Minelayer

Sep 39 to Jul 43

1 ship - construction suspended

9 Improved Sokuten Class

Subchaser

Jul 39 to Mar 41

4 No. 13 Class Subchasers

Minesweeper

Sep 40 to Mar 43

6 No. 19 Class Minesweepers

Emergency Netlayer

Dec 40 to Not 41

Wakataka

Tanker

Mar 42 to May 43

Sunosaki

Note: Although the budget approved by Diet showed a total of 83 ships to be constructed, the Navy decided to build only 80 ships and to use the extra appropriations to construct two super battleships. Later, it was found that this plan

not practical and Battleship 110 was converted into the Carrier Shinano, while, after suspending construction on Battleship 111 in December 1940, lt was finally dismantled in March 1943.

--21--

not have complete faith in this ambitious program, however, it was felt necessary to attempt this goal in order to instill the "air strength first" idea into the naval armament plan. About this time aircraft production had made unexpected progress as a result of the China Incident. Taking advantage of this momentum, this plan aimed at developing the low aircraft production capacity of Japan at any cost to carry out the Fourth Replenishment Plan. Therefore, subsequent to the commencement of this plan, it was made a rule to give priority to the naval air armament plan within the limits of scheduled manpower, materials and facilities. Accordingly, from that time forward, naval air armament was not restricted for financial reasons. The building up of air power, however, was retarded by the fact that, in spite of the vision of the few who could see the tremendous importance of air power, with many the basic idea of huge warships and big guns as a nucleus of sea power, with air power as auxiliary strength, still predominated.

With the Third Replenishment Plan almost completed, but before the Fourth Replenishment Plan was completely drafted, in October 1938, naval air armament under the Fourth Replenishment Plan was begun. The plan made unexpectedly good progress due to strong advocacy of "air strength first" in naval armament. Production facilities were expanded and aircraft production techniques were much improved.

--22--

When the situation became critical in August 1941, the order was given to advance the plan by one year, changing it to a four-year plan to be completed in the fiscal year 1942. Not only was this plan completed as revised, but, during this time, a large amount of the strength lost due to the China Incident was replaced. From 1941 onward, although each supplementary armament plan and each new armament plan was put into effect in advance, they were rarely completed in the specified time.

The number of aircraft completed in the fiscal years 1940 and 1941 to replace the expended aircraft was estimated to be:

Carrier fighters

75

Carrier bombers

37

Carrier attack planes

36

Reconnaissance seaplanes

43

Medium attack planes

102

Total

293

Thus, from a practical angle, the air strength of the Japanese Navy at the time of the outbreak of the Pacific War was almost equal to the expected strength at the time of the completion of the Fourth Replenishment Plan. Details of the plan in connection with other war preparations and armament plans will be mentioned in monograph No 160.

Compared with the preparation and replenishment of the above air groups, the expansion of aircraft production and the training of air personnel lagged far behind. The greatest difficulties encountered in air preparation and armament throughout the Pacific war, and even in pre-war days, were the poor aircraft equipment and the shortage of well-trained air personnel.

--23--

Appendix I

Third Replacement Plan

Ship Construction

Tonnage
per Ship
(Standard Displacement)

Number of
ships

Total Tonnage

Speed
(knots)

Cruising
Range

Principal Armament

Remarks

Battleships

64,000

2

120,000

27

16 knots

7,200 nautical miles

460mm guns

9

155mm guns

12

127mm Dual Purpose guns

12

Aircraft

6

Aircraft Carriers

20,000

2

60,000

34

18 knots

9,700 nautical miles

12.7mm Dual Purpose guns

16

Aircraft-96/Fighter/Primary

18

Fighter/Secondary

8

Bomber/Primary

54

Bomber/Secondary

18

Seaplane

Tender

9,500

1

9,500

22

16 knots

8,000 nautical miles

140mm guns

6

Originally planned for minelayers

Reconnaissance Seaplane Primary

20

Reconnaissance Seaplane Secondary

5

Facilities for boarding Type A
Midget Submarines

Minelayer

4,000

1

4,000

21

14 knots

6,400 nautical miles

127mm guns

4

Depth Charge Thrower

1

Mines

600

Minelayer (Emergency Net Layers)

1,600

2

3,200

20

14 knots

4,100 nautical miles

40mm Machine guns

2

Depth Charge Thrower

1

Antisubmarine Nets

24

Escort Ships

860

4

3,440

20

14 knots

8,000 nautical miles

120mm guns

3

Depth Charge Thrower

1

Gunboats (Class A)

990

2

1,980

19.5

14 knots

2,500 nautical miles

120mm Dual Purpose guns

3

Gunboats (Class B)

320

2

640

17

14 knots

1,400 nautical miles

Torpedo Tube

1

Destroyers

2,000

15

30,000

35

18 knots

5,000 nautical miles

120mm guns

6

The approved budget was for 18 vessels. The budget for three of them was diverted to battleship construction.

Torpedo Tubes

8

Submarines

(Class A)

2,200

2

4,400

Surface 23.5

16 knots

16,000 nautical miles

140mm gun

1

Torpedo Tubes

6

Aircraft

1

Submarines

(Class B)

1,950

6

11,700

Surface

23.6

16 knots

14,000 nautical miles

140mm gun

1

The approved budget was for 12 vessels. The budget for one of them was diverted to battleship construction.

Torpedo Tubes

6

Aircraft

1

Submarines

(Class c)

2,100

5

10,900

Surface

23.4

16 knots

,000 nautical miles

140mm gun

1

Torpedo Tubes

8

Minesweepers

630

6

3,700

20

14 knots

2,000 nautical miles

120mm guns

2

Depth Charge Throwers

2

Naval

Transport

10,360

1

10,360

14

14 knots

8,000 nautical miles

120mm Dual Purpose guns

(Equipped with facilities for the transportation of 460mm gun)

2

Survey ship

1,400

1

1,400

20

16 knots

8,000 nautical miles

120mm guns

4

Light

Minelayers

720

5

3,600

20

14 knots

2,000 nautical miles

80mm Dual Purpose guns

1

Depth Charge Throwers

2

Subchasers

290

9

2,610

20

14 knots

2,000 nautical miles

40mm Machine guns

TOTAL

66

269,510

--25--

Aircraft Preparation - Land-based Air Croup

Classification

Number of Units

Number of Aircraft

Total Number of Aircraft

Per Unit

Scheduled

Primary

Secondary

Primary

Secondary

Operational Air Group

Carrier Combers

1

12

4

12

4

16

Land Attack Planes

2.5

12

4

30

10

40

Reconnaissance Seaplanes

1.5

8

4

12

6

18

Medium Flying Boats

1

4

2

4

2

6

Total

6

58

22

80

Training Air Group

Primary

1

12

18

12

18

30

Intermediate

5

12

12

60

60

120

Combat Trainers

2

12

4

24

8

32

Total

8

96

86

182

GRAND TOTAL

14

154

108

262

NOTE: The total of 14 units in the above chart is some times regarded as included in the Third Replenishment Plan, because the completion of shipboard air groups mas delayed along with the progress of ship construction.

Shipboard Air Strength

Classification

Number of Aircraft

Total
Number of
Aircraft

Primary

Secondary

Carrier Fighters

48

12

60

Carrier Bombers

144

48

190

Reconnaissance Seaplanes (Ship board)

38

4

42

Total

230

64

294

NOTE: There was a budget appropriation for carrier bombers but for attack planes. This was a budget problem with the appearance of new carrier bombers.

--27--

Appendix II

Expected Air Strength at the Time of the Completion of the Third Replenishment Plan [two page table]

Aircraft type

Group

Operational air group

Plan

Former Plan (after reorganization)

First Plan

Second Plan

Third Plan

Total

Former Plan

(after reorganization)

First Plan

Classification of Number

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total.

Carrier fighters

1.5

18\6

24

1.0

12\4

16

2.5

30\10

40

5.0

60\20

80

0.58

6\2

8

1.0

12\4

16

Carrier bombers

1.0

12\4

16

1.0

12\4

16

Carrier attack planes

1.0

12\4

16

3.5

42\14

56

4.5

54\18

72

0.5

6\2

8

3.0

36\12

42

Carrier Reconnaissance planes

2.0

24\8

32

Medium attack planes

1.0

9\3

12

2.5

30\10

40

2.5

30\10

40

6.0

69\23

92

Large attack planes

1.5

12\3

15

12\3

15

Reconnaissance planes

2.5

20\10

30

1.0

8\4

12

1.5

5.0

40\20

60

2.0

16\8

24

Shipboard Reconnaissance Seaplanes (other than carriers)

Small flying boats

1.5

12\6

18

1.J

12\6

18

0.5

4\2

4

Medium flying boats

3.0

12\6

18

1.0

4\2

6

4.0

16\8

24

Large flying boats

1.0

2\0

2

1.0

2\0

2

2.0

4\0

4

Primary trainers

3.0

30\54

90

Intermediate trainers

Combat trainers

13\4

Research planes

1.0

4

16

0.5

8\2

8

Total

7.5

71\29

100

9.5

76\28

104

7.5

74\23

97

6.0

58\22

80

30.5

279\102

381

9.0

104\80

184

4.5

54\18

72

Armament Plan

Classification\Plan

Former Plan

First Plan

Second Plan

Third Plan

Total

Land-based operational air strength

100

104

97

80

381

Land-based training air strength

184

72

8

182

446

Carrier and shipboard air strength

510

284

294

1,088

Total

970

389

556

1,915

 

 

 

Land-based air group

Shipboard air strength

Grand Total

Training air group

Total

Second Plan

Third Plan

Total

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Number of Units

Number of aircraft

Ships up to and in First Plan

Second Plan

Third Plan

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary\ Auxiliary

Total

Primary

Auxiliary

Total

0.5

4\2

8

2.0

24\8

32

7.0

84\28

112

81\30

111

36\18

54

48\12

60

165\60

225

249

86

337

1.0

12\4

16

144\48

192

144\68

192

156

52

208

3.5

42\14

56

8.0

96\32

128

154\60

214

84\42

126

240\102

342

336

134

470

2.0

24\8

32

2.0

24\8

32

24

8

32

6.0

89\23

92

69

23

92

1.5

12\3

15

12

3

15

2.0

16\8

24

7.0

56\28

84

20\0

20

72\18

90

92\8

110

148

46

196

122\41

163

14\0

14

38\4

42

174\45

217

174

45

219

0.5

4\2

6

2.0

16\9

24

14

8

24

4.0

16\8

24

14

8

24

2.0

4\0

4

4

0

4

1.0

12\8

30

4.0

48\72

120

4.0

48\72

120

48

72

120

5.0

60\60

120

5.0

60\60

120

5.0

60\60

120

60

60

120

2.0

24\8

32

2.0

24\8

32

2.0

24\8

32

24

8

32

1.5

18\6

24

1 5

18\6

18

6

24

0.5

6\2

8

8.0

96\86

182

22.5

260\186

446

53.0

539\288

379\131

510

206\78

284

230\64

294

815\273

1,088

1,354

561

1,915

--29--

Appendix III

Outline of the First War Preparations Analysis Conference

23 August 1937

Matters for Consultation Concerning War Preparations

Arrangements and Explanations

Policy

In anticipation of the China operations being protracted, war preparations which are of direct necessity will be completed. In addition, part of the war preparations required for sea operations will be accelerated in order to brush off interference, if any, of the Three Powers.

Outline

Surface Units

The completion of the following ships being re-equipped or reinforced will be accelerated. Akagi, Yamashiro, Mogami, Submarine I-71

The re-equipment of ships which are slated to be completed by the end of 1937 will bo continued as scheduled. The re-equipment of four ships mentioned in the left column is slated to be completed in the first half of 1938, and the date of completion is set as the end of January 1938 with the exception of the Akagi, which requires special preparation in order to strengthen sea-air strength.

The construction of the following ships will be accelerated: Soryu, Tsurugizaki, Takasaki. Chitose. Subchasers and other ships nearing their completion in accordance with the Naval Replenishment Plan for the fiscal year 1937.

Besides the above, the existing surface units of the strength included in the war organisation plan for the fiscal year 1937 will be equipped so as to execute operations effectively.

Emphasis will be laid on the acceleration of preparation of ships under repair or under overhaul. However, obsolescent ships such as the Hirato, Yahagi and Karazaki are excluded from such preparation.

Necessary ships will be requisitioned.

Converted seaplane tenders 4; converted combined collier and oil tanker 1; converted

--31--

Converted aircraft carriers equipment and materials required for conversion work will be prepared for three ships of Asama Maru class.

gunboats 4; converted ships Ko 12; converted subchasers 4.

Motors to be used for operating lifts, the lifts themselves, other materials and blueprints for conversion plans.

Air Strength

Medium attack planes and their equipment. Manufacturing and completion of the above a according to Navy Secretariat Secret Document No 2893, will be accelerated to the utmost.

Other aircraft and their equipment. The losses of the existing strength will be replenished. Aircraft and its equipment will be completed to achieve strength on wartime footing for the fiscal year 1937.

Besides those now being assembled, 75 aircraft will be completed in 1937.

A monthly output of 120 aircraft is scheduled. It will be increased to 350 by the end of the fiscal year 1937.

Defense

It will be completed in accordance with the Secondary and the Tertiary Defense in the Essentials of Naval Defense Program for the fiscal year 1937.

Facilities

Air bases

Effort will be made to complete immediately air bases

under construction and other necessary facilities.

Communications facilities

Communications facilities necessary for the above-mentioned defense will be completed.

The air bases mentioned on the left will be established chiefly on South Sea Islands and the Kuriles. Places necessary to establish new air bases are Genzsan and Chitose (in Hokkaido).

To be established: Second Transmitting Station of Shanghai Land Combat Unit; Harbin Radio Receiving Substation; Rashin Communications Unit; Niigata

Radio Finder Station; Mikuriya Radio Direction Finder Station. Completion of Equipment for Communications Units.

Construction and repair facilities

Efforts will be made to complete facilities required for the prepara-

--32--

tion of above strength and of the Sixth Expeditionary Preparation Materiel.

Personnel

Efforts will be made to train the personnel required for the operation and maintenance of the above strength and facilities.

Personnel on First and Second Reserve Lists to be called to active service. Aircraft personnel to be trained.

Preparation of Expeditionary Materiel

Based on the above strength, preparations will be made for the completion of materiel for the opening of hostilities in accordance with the Expeditionary Preparations Regulations for the fiscal year 1937. Every effort will be made for the procurement and preparation of fuel, raw materials, bombs and other necessary arms.

Air defense equipment: Dual purpose guns; machine guns; range finders; sound locators.

Anti-Submarine equipment:

Mines; antisubmarine nets with mines; hydrophones.

Shells, powder and other equipment.

--33--

Appendix IV

Fourth Replenishment Plan of the Naval Armament Completion Plan Aircraft Preparation - Land-based Air Group

Classification

Operational air groups

Training air groups

Transport planes

Total

Number of Units

34.5

40.5

75

Number of aircraft

566

877

35

1,443 Plus 35

NOTE: If the strength of former plans is included, the total strength will amount to 128 units (2270 aircraft) 65 operational units (947 aircraft) and 63 training units (1323 aircraft) and 35 transports.

Details of this air strength are:

Classification

Number of Units

Number of aircraft

Per Unit

Total

Primary

Secondary

Total

Primary

Secondary

Total

Operation air group

Carrier fighters

6.5

12

4

16

78

26

104

Carrier attack alarms

2.0

12

4

16

24

8

32

Medium attack Planes

18.5

12

4

16

222

74

296

Reconnaissance seaplanes

7.5

8

4

12

60

30

90

Medium flying boats

Reorganized Two groups reduced

8

4

12

No increase or decrease in number

Large flying boats

Reorganized Two groups increased

8

4

12

28

16

44

Total

34.5

412

154

566

Training air group

Primary trainers

7.5

12

18

30

90

135

225

Intermediate trainers

15.5

12

12

24

186

186

372

Combat trainers

17.5

12

4

16

210

70

280

Total

40.5

486

391

877

Transport planes

Large transport planes

24

Medium transport planes

11

Total

35

GRAND TOTAL

75.0

898

545

1,443 Plus 35

--34---

NOTE: Approval was obtained to include the 3.0 medium attack plane units planned in the 1938 • Extraordinary Military Expenditure in the 18.5 medium attack plane units in this plan.

Subtracting 597 trainers from 1443 aircraft, there were 846 operational aircraft in all. This number corresponded to the number of navy aircraft in the Second Vinson Plan.

Shipboard Air Strength

Classification

Number of aircraft

Remarks

Primary

Secondary

Total

Carrier fighters

24

12

36

Carrier aircraft

Carrier bombers

24

12

36

"

Carrier attack planes

36

18

54

"

Reconnaissance seaplanes

48

0

48

Shipboard aircraft

Total

132

42

174

NOTE: The first completion expenditure for shipboard air strength is included in the ship budget in each armament plan.

It was planned to organise air groups at Komatsushima, Tainan, Misawa, Katori, Tokushima, Matsushima, Shinchiku, Mikawa Bay, Chitose and Genzan (as well as eight training air groups). However, the plan was to be changed as occasion demanded in accordance with the establishment of airfields, training programs or other situations that might arise.

--35--

Appendix IV(Cont'd)

Fourth Replenishment Plan of the Naval Armament Completion Plan - 1939

Ship Construction

Tonnage (Displacement

tonnage)

Number

Total Tonnage

Speed

(knots)

Cruising Range (knots-nautical miles)

Principal Armament

Note

Battleships

64,000

2

128,000

27.0

16-7,200

460mm guns

9

One ship's construction suspended and ship dismantled.

One a ship converted to carrier.

155mm guns

12

100m dual purpose guns

12

Aircraft

6

Carrier

30,360

1

30,360

33.3

18-10,000

100m dual purpose guns

6

Aircraft

52

Cruisers (Class B)

6,500

4

26,000

35.0

18-6,000

150mm guns

6

80mm dual purpose guns

4

Torpedo tube

8

Cruisers (Class C)

8,000

2

16,000

35.0

18-8,700

155mm guns

6

One ship's construction suspended

100m dual purpose guns

8

Destroyers (Class A)

2,000

16

32,000

35.0

18-5,000

127mm guns

6

The budget for 18 destroyers was approved, but the amount for the ten destroyers was diverted to the construction of super-battleships.

Torpedo tubes

8

Destroyers (Class B)

2,700

6

16,200

33.0

18-8,000

100m dual purpose guns

8

Torpedo tubes

4

Submarines (Class A)

2,200

1

2,200

Surface Speed

23.5

Surface Speed 16-16,000

140mm gun

1

Torpedo tubes

6

Aircraft

1

Submarines (Class B)

1,950

14

27,300

23.6

16-14,000

140mm gun

1

The budget for 15 submarines was approved, but the amount for one submarine was diverted to the construction of super-battleships.

Torpedo tubes

6

Aircraft

1

Submarine (Navy Large Type)

1,500

10

15,000

23.1

16-8,000

25mm machine guns

4

Torpedo tubes

6

Training ship

5,800

1

5,800

18.1

12-10,000

140mm gun

4

127m dual purpose guns

3

Flying boat tender

4,650

1

4,650

19.1

14-8,000

127mm dual purpose guns

4

(Facilities for landing 1 large type flying boat)

Minelayer

1,600

1

1,600

20.0

14-3,000

80mm dual purpose guns

2

Depth charge throwers

1

Light

minelayers

720

10

7,200

20.0

14-2,000

80mm dual purpose guns

1

Depth charge throwers

2

Minesweepers

630

6

3,780

20.0

14-2,000

120mm gun

1

Large minesweeping equipment

Subchasers

440

4

1,760

16.0

14-2,300

80mm dual purpose guns

1

Depth charge throwers

2

Oil tanker

4,460

1

4,460

18.0

14-9,000

120mm dual purpose guns

2

Gasoline supply equipment for an aircraft carrier at sea.

Total

60

322,310

--37--

 

Japanese Monograph No. 160

OUTLINE OF NAVAL ARMAMENT AND PREPARATIONS FOR WAR

Part III

PREPARED BY MILITARY HISTORY SECTION HEADQUARTERS, ARMY FORCES FAR EAST

DISTRIBUTED BY OFFICE OF THE CHIEF OF MILITARY HISTORY DEPARTMENT OF THE ARMY

This is the third of a series of six monographs in regard to Japan's naval armament in preparation for and during the Pacific War.

Additional monographs covering Japan's naval armament plans are:

Mono No

Outline of Naval Armament and Preparations for War, Part I

145

Outline of Naval Armament and Preparations for War, Part II

149

Outline of Naval Armament and Preparations for War, Part IV

169

Outline of Naval Armament and Preparations for War, Part V

172

Outline of Naval Armament and Preparations for War, Part VI

174

--iii--

Preface

Through Instructions No. 126 to the Japanese Government, 12 October 1945, subject: Institution for War Records Investigation, steps were initiated to exploit military historical records and official reports of the Japanese War Ministry and Japanese General Staff. Upon dissolution of the War Ministry and the Japanese General Staff, and the transfer of their former functions to the Demobilization Bureau, research and compilation continued and developed into a series of historical monographs.

The paucity of original orders, plans and unit journals, which are normally essential in the preparations of this type of record, most of which were lost or destroyed during field operations or bombing raids rendered the task of compilation most difficult; particularly distressing has been the complete lack of official strength reports, normal in AG or G3 records. However, while many of the important orders, plans and estimates have been reconstructed from memory and therefore are not textually identical with the originals, they are believed to be generally accurate and reliable.

Under the supervision of the Demobilization Bureau, the basic material contained in this monograph was compiled and written in Japanese by former officers, on duty in command and staff units within major units during the period of operations. Translation was effected through the facilities of Allied Translators and Interpreters Service, G2, General Headquarters, Far East Command.

This Japanese Operational Monograph was rewritten in English by the Japanese Research Division, Military History Section, General Headquarters, Far East Command and is based on the translation of the Japanese original. Editorial corrections were limited to those necessary for coherence and accuracy.

--v--

TABLE OF CONTENTS

Chapter

Page

I

GENERAL SITUATION

1

Preparation of Armament Against the United States

3

First Requisition, Conversion and Equipment of Vessels

6

Extraordinary Supplementary Armament Plan

7

Urgent Armament Plan

15

Second Requisition and Equipment of Vessels

29

Acceleration of other War Preparations

30

War Preparations Upon Decision to Go to War

31

Organization of Special Naval Units

32

Progress of Armament and Other War Preparations at the Time of the Outbreak of War

34

II

OUTLINE OF THE FIFTH AND SIXTH NAVAL ARMAMENT REPLENISHMENT PLANS

41

 

Charts

 

No. 1

Extraordinary Supplementary Armament Plan
Other Supplementary Armament Plans between

the Fourth Armament Replenishment Plan
and the Urgent Armament Plan

9

2

Progress of Shipbuilding

13

3

Urgent Armament Plan

17

4

Urgent Armament Plan Approved Budget

21

5

Urgent Armament Plan Progress of Shipbuilding

23

6

Air Strength at time of Outbreak of War

37

--vii--

7

Roster of Naval Officers at time of Outbreak of War

39

8

Fifth Armament Replenishment Plan

42

--viii--

Chapter I

General Situation

With the outbreak of World War II on 1 September 1939, the United States policy appeared to be to assist Great Britain and France in every way possible. The arms embargo was lifted at the beginning of November 1939, and, at the same time, the construction of an additional 40 US destroyers was approved. To offset the preponderance of German submarines in the spring of 1940, the United States leased 50 escort destroyers to Great Britain and extended positive aid in regard to the strengthening of the escort provided Europe-bound merchant ships.

In November 1939, having been notified of the commencement of the Japanese Fourth Armament Replenishment Plan, the United States Navy submitted to Congress the Third Vinson Plan, and, on 4 June 1940, it was signed by the President. The plan called for the construction of 3 aircraft carriers, 8 cruisers, 52 destroyers and 32 submarines, having a total tonnage of 400,000 tons. Also included in the plan was the construction of auxiliary vessels amounting to 125,000 tons, making a total tonnage of 525,000 tons. In addition, provision was made for 6,000 Navy planes and 36 flying boats. The appropriations for this plan amounted to $1,300,000,000, and the year of completion was set at 1944. It was estimated that the United States would have a main strength totaling more than 2,100, 000 tons, with a nucleus of 23 battleships, when this plan was completely realized.

--1--

In the spring of 1940, at the same time as the Third Vinson Plan began to get under way, the United States Navy decided to station permanently in the Hawaiian area the main force of the fleet then bound for that area to take part in large-scale maneuvers.

It was felt that the tightening of the political and economic encirclement of Japan by the United States, Great Britain, the Netherlands, Australia and China, coupled with the protraction of the China Incident, was making Japan's position more and more untenable. In order to surmount this difficulty, Japan took steps to strengthen her tripartite ties and to advance to the south. This caused the Anglo-American bloc to stiffen their attitude toward Japan. To cope with this critical situation, the Japanese Navy carried out various emergency measures. In 1941, to counteract the Third Vinson Plan, the Fifth Armament Replenishment Plan was adopted. (See Chapter II) However, on 19 June 1941, the astronomical United States' Stark Plan was approved. The Stark Plan was a two-ocean fleet plan with a 70 percent increase in the total tonnage of naval vessels and an increase in Navy planes to 15,000. The appropriation for this 6-year plan was $10,000,000,000.

Although it was realized that the fulfillment of the Fifth Armament Replenishment Plan would be most difficult from the standpoint of finance, materials and equipment, Japan considered it necessary to continue in the naval armament race, which resulted in the drafting of the Sixth Armament Replenishment Plan. (See Chapter II)

--2--

The strained relations between Japan and the United States led the navies of the two nations to compete in an unlimited and endless armament race.

Preparation of Armament Against the United States

The armament policy of the Japanese Navy had hitherto been based on the requirements of the national defense policy which aimed to maintain a strength in the ratio of 7:10 with the United States. The object of the national defense policy was to guarantee the security of the nation by securing the supremacy of sea and air in the Western Pacific. The 7:10 ratio was based on the tactical principle accepted at that time by the navies of all countries, which concluded that the strength of the offensive force must be at least 50 percent superior to that of the defensive force. While a navy of 7:10 ratio would be insufficient for offensive warfare, it would be enough for defensive warfare.

Because of the completion of the naval armament replenishment plans in the United States, the Japanese Navy's policy for maintaining the 7:10 ratio with the United States became futile, and it was estimated that in a short space of time the ratio of Japan's strength would decrease to less than 6:10 with the United States. Consequently, strenuous efforts were made to offset the quantitative deficiency by such means as effective armament preparations, skilled strategy and an effort to meet quantity with quality. Toward the end of 1940 Japan was forced to revise the armament policy generally as follows:

--3--

As it was predicted that in the near future the ratio of battleships would become less than 5:10 with the United States, the idea of meeting quantity with quantity was abandoned. It was decided that by building such huge battleships as the Musashi and Yamato quantitative deficiency would be balanced by the superior power of individual vessels. In accordance with the sudden change in the situation at the end of 1941, however, the construction of battleships, other than the almost completed Musashi and Yamato, was suspended. After the defeat in the Midway Battle in June 1942, it was decided to complete the reconstruction of the battleship Shinano into an aircraft carrier by the end of 1944.

Aircraft Carriers

Although at the end of 1940 there was no real difference in strength between the United States and Japan in regard to this type of vessel, there was every possibility that the United States would build more aircraft carriers in the near future. Therefore, without adhering to the tonnage ratio, Japan adopted a policy of creating parity on the number of vessels built by the United States. Finally, having exhausted her capacity for shipbuilding, Japan decided to convert first-class merchant ships into aircraft carriers. This plan was studied for some years before being put into operation. Cruisers

It was felt that there would be no difficulty in maintaining the 7:10 ratio with the United States in regard to cruisers, as

--4--

Japan was in quite a favorable position in regard to this type of vessel, especially in regard to heavy cruisers. It was decided, therefore, that the Japanese Navy policy of giving priority to superiority of fire power, torpedo power and speed should be continued.

Destroyers

Although the ratio with the United States in regard to destroyers was approximately 7:10, it was felt that within a short period of time the difference in strength would be great, because of the United States' gigantic armament plans, and her capacity to reduce the time required in shipbuilding. Another factor was that the Japanese Navy required their destroyers to carry heavy torpedo equipment to be used for night combat. This meant that the destroyers had to be larger, and, in consequence, not able to build as many.

Submarines

From the start, the quality and number of this type of vessel was not based on the ratio with the United States. As the Japanese Navy employed these vessels chiefly in interception actions and fleet warfare, they were all large, but they were few in number. In order to remedy this defect, midget submarines were built. Aircraft

Until the Third Armament Replenishment Plan, which counteracted the Second Vinson Plan, Japan aimed generally at an equal number of planes with the United States, but because no measure could be taken to cope with the Third Vinson Plan, which called for 6,000 Navy planes lost in the China Incident, it became more and more difficult

--5--

to maintain the ratio. By estimating the potential air strength of the United States which could be engaged in an offensive in the Far East, the minimum strength required to intercept this force was to be maintained. There was a tendency, however, to underestimate the power of the United States, and the Japanese Navy hoped that the lack of planes could be compensated by the mobility of the forces stationed at dispersed air bases.

First Requisition, Conversion and Equipment of Vessels

At the outbreak of the China Incident, vessels were requisitioned and equipped as part of the preparations for war. The Japanese Navy being unable to take any measures to counteract the Third Vinson Plan, decided on 15 November 1940 to requisition a total of 550,000 ship tons. These ships would be converted into aircraft carriers, transports, cruisers, gunboats and other auxiliary vessels as well as used as general naval transports. The work was undertaken gradually and, for the most part, was completed within six months.

In contrast to the nine aircraft carriers built under the Vinson Plans and supplementary armament plans, Japan's Third and Fourth Replenishment Plans made provisions for only three carriers. In consequence, in order to maintain parity, Japan had to make further plans. As a result, it was decided to convert first-class merchant ships. The Kasuga Maru was requisitioned and the Isumo Maru and Kashiwara Maru were purchased. The work of converting them into aircraft carriers was started in early 1941. The Taiyo (Kasuga Maru)

--6--

15,000 tons was completed 25 August 1941; the Junyo (Kashiwara Maru) 19,000 tons was completed 3 May 1942, and the Hiyo (Izumo Maru) 19,000 tons was completed 31 July 1942. It was planned that after careful study and preparation other merchant ships and some warships would be converted into aircraft carriers in order to increase the aircraft carrier strength.

In accordance with the Fourth Armament Replenishment Plan, the keels of the battleships Shinano and Kii were laid at Yokosuka and Kure Naval Yards respectively, and their construction up to double-bottoms was completed. The work was suspended temporarily on account of the delay in the construction of armour, and later, because of the major changes in armament and war preparation plans affected by the outbreak of war, it was decided to discontinue construction. Because of the sudden decrease in carrier strength caused by losses in the Battle of Midway, however, it became necessary to convert the Shinano into an aircraft carrier.

Extraordinary Supplementary Armament Plan

The Navy Ministry and the Naval General Staff agreed on the details of the Fifth Armament Replenishment Plan in order to counteract the Third Vinson Plan, but it looked as though there might be some difficulty in obtaining the necessary finances, materials and plants from the Finance Ministry, Planning Board and War Ministry respectively.

It was thought wise for the Naval General Staff to consult the Army General Staff in regard to the Fifth Armament Replenish-

--7--

ment Plan. The Army General Staff agreed to the plan under the following conditions: that it should be discussed again if it showed signs of hampering the established armament plan of the Army; that the Army would deliberate the matter of allocation of materials included in the material mobilization plan; and that it would decide the allocation of necessary manpower. Since the outbreak of the China Incident, the Japanese Navy had recognized the necessity for giving priority to the Army in regard to armament replenishments, in consideration of the nature of the operations. Unless priority was granted to the Fifth Replenishment Plan, however, it would be impossible to realize the plan. Therefore, the conditions imposed by the Array made it clear that they were rejecting the plan. From this time forward there was a constant struggle between the two services in regard to munition production.

The Japanese Navy felt keenly the necessity for taking extreme measures in order to accelerate their war preparations, and in May 1941 it established, and immediately put into execution, the Extraordinary Supplementary Armament Plan, known in Japanese as the "Maru Rin." (For details see Chart 1.)

Additional Supplementary Plans were placed into effect between the Fourth Armament Replenishment Plan and the Urgent Armament Plan and their progress, on the whole, was satisfactory. (See Charts 1 and 2)

There was no new plan for air armament. The air armament plan of the Fourth Armament Replenishment Plan had progressed compara-

--8--

Chart 1 - Extraordinary Supplementary Armament Plan

Standard Displacement per Vessel

Number of Vessels

Total Tonnage

Speed

Main Armament

Remarks

Submarines (Medium)

970

9

8,730

19.5 (Surface)

80mm gun

1

Approved budget the fiscal year 1941

General account: ¥196,424,750.00

25mm machine guns

2

Torpedo tubes

4

Submarines (Small)

525

9

4,725

14.2 (Surface)

25mm machine guns

2

Torpedo tubes

4

Gasoline tankers (Medium)

7,950

2

15,900

16.0

127mm gun

4

Gasoline tankers (Small)

4,460

4

17,840

16.0

120mm gun

2

Subchasers

440

16

7,040

16.0

80mm dual purpose gun

1

Auxiliary minesweepers

215

6

1,290

9.5

80mm gun

1

Approved budget the fiscal rear 1941

Extraordinary military expenditure: ¥21,030,000.00

Auxiliary minelayers

280

4

1,120

9.5

80mm gun

1

Refrigerator ships

920

3

2,760

14.0

80mm gun

1

Motor torpedo boats

20

4

120

35.0

25mm machine guns

2

Total

59

59,525

¥220,934,750.00

--9--

[--10-- blank]

Chart 1 - Other Supplementary Armament Plans between the fourth Armament Replenishment Plan and the Urgent Armament Plan

Standard Displacement per Vessel

Number of Vessels

Total

Speed

Main Armament

Remarks

Cable laying boats

1,564

4

6,256

14.0

80mm dual purpose gun

1

Approved budget the fiscal year 1939

Extraordinary military expenditure: ¥13,667,000.00 (of which ¥3,480,000.00 allotted to not or torpedo boats)

Refrigerator ship

920

1

920

14.0

80mm dual purpose gun

1

Refrigerator ship

640

1

640

13.0

80mm dual purpose gun

1

Suchasers

440

7

3,080

16.0

80am dual purpose gun

1

Approved budget the fiscal year 1940

Extraordinary military expenditure: ¥8,820,000.00

Training ship

5,800

1

5,800

18.0

140mm guns

4

Approved budget the fiscal year 1941

General account ¥7,660,000.00

127mm dual purpose guns

2

Torpedo tabes

4

--11--

[--12-- blank]

Chart 2 — Progress of Shipbuilding

Extraordinary Supplementary Armament Plan:

Type of Vessel

Class

Name of Vessel

Number of Vessels

Period of Construction

Remarks

Submarines (Medium)

Ro 35 Type

Ro 35 & others

9

Oct 41 to Dec 43

Submarines (Small)

Ro 100 Type

Ro 100 & others

9

Jun 41 to Apr 43

Gasoline tankers (med)

Ashizuri class

Ashizuri & others

2

Jul 41 to Nov 43

Gasoline tankers (small)

Sunozaki class

Takasaki

1

Jul 42 to Sep 43

Gasoline tankers (small)

Sunozaki class

3

Construction suspended

Subchasers

No 13 Type

No 24 & others

16

Hay 41 to Feb 43

Auxiliary Minesweepers

No 1 Type

No 1 & others

ft

Jun 41 to Oct 42

Auxiliary Minelayers

No 1 Type

No 1 & others

4

Jun 41 to Aug 42

Refrigerator ships

Kinozuki class

Hayasaki & others

3

Dec 41 to May 43

Motor Torpedo boat

No 1 Type

No 1 & others

6

Nov 41 to Dec 41

Total

59

56\3

May 41 to Dec 43

Completed

Other Supplementary Plans between the Fourth Armament Replenishment Plan and Urgent Armament Plan:

Type of Vessel

Class

Name of Vessel

Number of Vessels

Period of Construction

Remarks

Cablelayers

Kashima class

Kashima & others

4

Oct 39 to Aug 41

Refrigerator ships

Kinozaki class

Kinozaki & others

2

Oct 39 to Mar 41

Subchasers

No 13 Type

No 17 & others

7

Oct 40 to Nov 41

Training ship

Katori class

Yashiwara

1

Aug 41 to Oct 41

Construction suspended

Total

14

13\1

Oct 39 to Nov 41

Completed suspended

--13--

[--14-- blank]

tively well due to the stalemate in the China Incident with resulting small losses in aircraft. In addition, ¥100,000,000 was allotted for the immediate preparation and activation of 17 of the 93 units of the Training Air Group included in the Fifth Armament Replenishment Plan. (See Chart 8)

Urgent Armament Plan

At the liaison conference between Imperial General Headquarters and the Government, held on 2 July 1941, the "Outline of the National Policy of the Japanese Empire in connection with the Change of Circumstances," which emphasized the drive southward and the inevitability of war with the United States and Great Britain to achieve Japan's objective, was agreed upon. In order to comply with this policy, the Japanese Navy, being well aware of its great deficiency in armament as compared with the United States, realized that it was necessary to speed up war production. In the latter part of August 1941 it decided on the over-all execution of the Expeditionary Preparation Plan. As part of it, the Wartime Armament Preparation Plan was immediately enforced. This plan became known as the Urgent Armament Plan. (See Charts 3, 4 and 5)

In order to equip oil tankers to carry airplanes, an additional ¥10,264,000 was approved for 1944 (¥2,566,000 for each vessel). Because it was decided to construct an aircraft carrier of 12,500 tons instead of a cruiser, a further ¥10,610,000 was approved for 1945.

--15--

Chart 3 - Urgent Armament Plan

Type of Vessel

Number of Vessels

Total Tonnage
(Standard Displacement)

Speed

Main Equipment

Remark

Aircraft carrier

1

17,150

34

127mm dual purpose guns

12

UNRYU

25mm machine guns

31

Aircraft

49

Cruisers

2

24,400

35

200mm guns

10

After launching one cruiser converted into aircraft carrier (IBUKI Class), but conversion work suspended. Construction of 1 cruiser suspended.

127mm dual purpose guns

8

Torpedo tubes

14

Aircraft

3

Destroyers (Class A)

16

41,104

35

127mm guns

6

Construction of 8 destroyers suspended.

Torpedo tubes

8

Destroyers (Class B)

10

27,000

33

100mm dual purpose guns

8

Construction of 1 destroyer suspended.

Construction of 3 destroyers cancelled.

Torpedo tubes

4

Submarines (Class B)

6

13,110

Surface 23.6

140mm gun

1

Torpedo tubes

4

Aircraft

1

Submarines
(Class C)

6

13,060

Surface 23.6

140mm gun

1

Construction of 3 submarines cancelled.

Torpedo tubes

8

Submarines
(Medium)

12

11,412

Surface 19.7

80mm guns

1

Construction of 4 submarines cancelled.

Torpedo tubes

4

Submarines
(Small)

9

4,662

Surface 14.2

25mm machine guns

2

Torpedo tubes

4

Seaplane tender

1

4,620

19

127mm dual purpose guns

4

Construction suspended.

(Installation for carrying one large flying boat)

--17--

[--18-- blank]

Urgent Armament Plan (Cont'd)

Type of Vessel

Number of
Vessels

Total
Tonnage
(Standard
Displacement)

Speed

Main Equipment

Remark

Escort ships (Class B)

16

15,040

19.7

127mm dual purpose gun

1

120mm dual purpose gun

1

Depth charge throwers

2

Escort ships (Class A)

14

12,040

19.7

120mm guns

3

Depth charge thrower

1

Minesweepers

28

18,200

20

120mm guns

3

Construction of 17 minesweepers cancelled.

Large sweep cables

6

Auxiliary

16

3,360

95

80mm gun

1

Light minelayers

14

10,080

20

80mm dual purpose gun

1

Construction of 13 minelayers cancelled.

Depth charge throwers

2

Subchasers

20

8,800

16

80mm dual purpose gun

1

Construction of 1 subchaser cancelled.

Depth charge throwers

2

Auxiliary subchasers (wooden)

100

13,000

11

13mm machine gun

1

Motor Torpedo boats

18

1,350

29.5

Torpedoes

12

Construction of 3 torpedo boats suspended.

Construction of 7 torpedo boats cancelled.

Oil tanker

1

18,850

Construction cancelled.

Oil tanker

2

36,800

16.5

120mm dual purpose gun

3

Later equipped to carry 6 airplanes.

Oil tanker

1

6,000

Construction cancelled.

Total

293

300,058

--19--

[--20-- blank]

Chart 4 — Urgent Armament Plan

Approved Budget

Type of Vessels

Tonnage

Number
of Vessels

Cost of one
Vessel

(Unit of
¥1,000)

Total
Cost

(Unit of
¥1,000)

Cruisers

12,000

2

60,000.0

120,000.0

Aircraft Carrier

17,100

1

87,039.0

87,039.0

Destroyers (Class A)

2,570

16

17,424.6

278,793.6

Destroyers (Class B)

2,980

10

17,820.4

178,204.0

Submarines (Class B)

2,280

12

20,497.2

245,966.4

Submarines (Medium)

1,000

12

7,920.0

95,040.0

Submarines (Small)

550

9

4,713.5

42,421.5

Flying Boat Tender

11,00

1

47,410.0

47,410.0

Escorts

1,200

30

5,112.0

153,360.0

Light Minelayers

720

14

4,334.4

60,681.6

Minesweepers

700

28

3,738.0

104,664.0

Auxiliary
Minesweepers
(Fishing Boat Type)

300

16

1,431.0

22,896.0

Subchasers

400

20

2,921.6

58,432.0

Auxiliary

Subchasers

(Wooden)

100

100

780.0

78,000.0

Oil Tankers

18,400

4

14,720.0

58,880.0

Motor Torpedo Boats

100

18

2,262.0

40,716.0

Total

293

1,672,504.1

--21--

[--22-- blank]

Chart 5 - Urgent Armament Plan

Progress of Shipbuilding

Type of Vessel

Class

Name of Vessel

Number of Vessels

Period of
Construction

Remarks

(Total)

293

228

Completed

7

Dec 41 to Apr 45

Work suspended

58

Construction cancelled

Cruisers

Suzuka class

Ibuki

2

1

Apr 42 to Mar 45
(Converted into aircraft carrier)

Work for conversion into aircraft carrier suspended

1

Jun 42 to Sep 42
(suspended)

Work suspended

Aircraft carrier

Remodeled Hiryu class

Unryu

1

Aug 42 to Aug 44

Seaplane tender

Akitsushima class

Chihaya

1

Jul 42 to Oct 42
(suspended)

Work suspended

Oil tanker

Kazahaya class

Kazahaya and others

4

2

Oct 42 to Apr 44

(Large)

1

Construction suspended

(Small)

1

Construction cancelled

Escort ships (class A)

Remodeled Shimushu class

Etorofu and others

14

Feb 42 to Feb 44

Escort ships (class B)

Mikura-class Ukuru-class

Mikura & others

16

Oct 42 to Nov 44

--23--

[--24-- blank]

Chart 5 - Urgent Armament Plan (Cont'd)

Type of Vessel

Class

Name of Vessel

Number of Vessels

Period of

Construction

Remarks

Destroyers(class A)

Yugumo class

Hayanami & others

16

8

Jan 42 to May 44

Yugumo class

8

Construction cancelled

Destroyers (Class B)

Akitsuki class

Shimotsuki & others

6

Jul 42 to Apr 45

Akitsuki class

Mitsutsuki & others

1

Jan 44 to Mar 44
(suspended)

Work suspended

Akitsuki class

Kiyotsuki & others

3

Construction cancelled

Submarine (Class B)

Type I-15

I-40 and others

6

Mar 42 to Feb 44

Submarine (Class C)

Type I-16

I-46 and others

6

3

Dec 42 to Aug 44

Type I-16

I-49 and others

3

Construction cancelled

Submarine (Medium)

Type Ro-35

Ro 44 and others

12

8

Feb 42 to Sep 44

Type Ro-35

Ro 51 and others

4

Construction cancelled

Submarine (Small)

Type Ro-100

Ro 109 and others

9

May 42 to Jan 44

Minesweepers

Type No 19

No 25 and others

28

11

Apr 42 to Jul 44

Type No 19

No 31 and others

17

Construction cancelled

--25--

[--26-- blank]

Chart 5 — Urgent Armament Plan (Cont'd)

Type of Vessel

Class

Name of Vessel

Number of Vessels

Period of Construction

Remarks

Subchasers

Type No 13

No 40 and others

20

19

Feb 42 to Jul 44

Type No 13

No 59

1

Construction cancelled

Light minelayers

Remodeled Hirashima class

Ajiro

14

1

Sep 43 to Jul 44

Ajiro class

Kamishima & others

13

Construction cancelled

Auxiliary minelayers

Type No 1

No 7 and others

16

Feb 42 to Oct 44

Auxiliary subchasers

Type No 1

No 1 and others

100

Dee 41 to Mar 44

Motor torpedo boats

Type A

No 10 and others

18

8

Jul 42 to Feb 45

Type No 10

No 18 and others

3

Mar 44 to Jun 44
(suspended)

Work suspended

Type No 10

No 21 and others

7

Construction cancelled

--27--

[--28-- blank]

as only three, months had elapsed since a part of the Fifth Armament Replenishment Plan (air section) had been put into effect, and that only after long deliberation and preparation, it was considered impossible to establish another supplementary plan to further augment air strength without causing confusion. As the Fourth Armament Replenishment Plan was progressing smoothly, it was decided to advance the date of completion of this plan by one year, the plan to be completed by the end of the 1942 fiscal year instead of 1943. The remarkable success of the Japanese Navy Air Force at the beginning of the Pacific War, and the idea of giving priority to air armament which resulted from the above decision, not only enabled the general completion of the Fourth Armament Replenishment Plan within the prescribed time, but also led to the realization of the Revised Fifth Armament Replenishment Plan.

Second Requisition and Equipment of Vessels

The vessels obtained through the First Requisition were almost completely equipped and were steadily being added to the fleet strength. Under the firm policy adopted in the summer of 1941, it was decided that an additional 600,000 tons of vessels would be requisitioned for use as converted vessels or for increasing the number of supply and transport vessels.

Included in the vessels requisitioned in accordance with this plan was the Nitta Maru, which was converted into the aircraft carrier Chuyo, and such ships as the Aikoku Maru and the Hokoku Maru, which later distinguished themselves as converted cruisers

--29--

raiding merchant shipping. Most of these vessels were completely equipped by the end of 1941, but, because it was to be used to carry the mission dispatched for the conference between President Roosevelt and Premier Konoye at Juneau, Alaska, the equipping of the Nitta Maru was not started until June 1942. It was completed as the converted aircraft carrier Chuyo (15,000 tons) in the latter part of November 1942.

Acceleration of Other War Preparations

The activation of the wartime organization of the Imperial Japanese Navy was proclaimed on 1 September 1941, and the Fleet rose to unprecedented strength.

Following this, all vessels were subject to necessary repair before going into action. It was scheduled that, because of the state of emergency, this work would be completed by the end of November. The greatest problem in connection with the execution of the Expeditionary Preparation Plan was the lack of war materiel. The war materiel stockpile planned during peacetime was virtually nothing compared to the quantity required by the huge number of. units organized and for the vessels to be constructed under this plan. There was available only 10 to 30 percent of the required quantity of such materiel as large bombs, Type 91 torpedoes, 20mm. machine guns and ammunition, all of which were vital to air war. Moreover, as the output of these items was very slow, it was believed that, within several months after the outbreak of war, stockpiles would be completely exhausted. Consequently, efforts

--30--

were made by the Navy Ship and Ordnance Department to increase the production of large bombs by converting shells of 16-inch guns, aircraft torpedoes and machine guns. At the same time, in order to increase the production of the Navy's weapons, and also to produce the strength called for in the Fifth Armament Replenishment Plan, preparations were made for the establishment of a number of Navy plants.

Although it was planned that the facilities for producing Type 93 torpedoes for surface vessels would be converted into those for Hype 91 torpedoes for aircraft, such a conversion required a complete change-over of materials, parts, machinery, etc. As no plans had been made during peacetime for this change-over, it was expected that there would be a blank period of several months before the increased production of Type 91 torpedoes could be achieved. However, this precaution prevented the disruption of supplies in regard to air operations after the outbreak of war.

War Preparations Upon Decision to Go to War

At the conference in the Imperial Presence held on 5 November 1941, a decision was reached on the "Outline for the Execution of the National Policy of the Empire," the main point of which was "to continue negotiations with the United States, but, in case no accord can be reached, a resolution to declare war will be adopted and preparations for operations will be undertaken. If a diplomatic settlement cannot be reached by the beginning of December, the decision to declare war will be made immediately."

--51--

As a result of this decision, actual responsibility concerning Navy war preparations was shifted from the naval administration authorities to the Supreme Command. In preparation for the unprecedented operations against the United States and Great Britain, the strongest and wealthiest nations in the world, in a theater covering almost the entire Pacific area, the Navy Ministry and all sections in charge of construction, repairs, replenishment and supply had to make all-out efforts under conditions of top secrecy.

With the launching of the United States' Stark Plan, Japan intended to set up the Sixth Armament Replenishment Plan. Just when the problem of how to adjust this plan with the Fifth Armament Replenishment Plan was being studied, the decision to declare war was reached. The Japanese Navy, therefore, ordered the construction of 32 submarines and one bombing target ship to be included in the Fifth Armament Replenishment Plan. At the same time, they ordered the increased production of both operational and training aircraft.

It was decided that an additional 500,000 tons of vessels, including the Yawata Maru, would be requisitioned for the purpose of supplementing the lack of all types of ships. Work was begun on the Yawata Maru in January 1942, and toward the end of May it was completed as the converted aircraft carrier Unyo (15,000 tons).

Organization of Special Naval Units Construction Battalions

Eight construction units were organized for the purpose of

--32--

constructing airfields in occupied territories. The plan was to dispatch five units to the Philippines, two to the Fourth Fleet area (Inner South Seas Area) and one to the Malay area. Regular

officers had no experience in this type of work. The units, therefore, were composed mostly of nonmilitary men who were compelled to carry a large amount of equipment with them. It was extremely difficult under the circumstances to conduct preparations and transportation at a top secret level. A meeting to discuss the duties of the leaders was delayed until after 10 November, and the men were dispatched toward the end of the month in order to join their assigned units in time for the operations.

Special Landing Units

Two units were organized and trained in each naval district. They were assigned to the respective invasion forces and dispatched rapidly.

The airborne units which were being trained in the Tateyama Sector under the command of the Yokosuka Natal District were the first of their kind in Japan. They were well trained and on 20 November were assigned to the Combined Fleet.

Fuel Exploitation Unit

As it was presumed that all oil refining facilities would be destroyed by the authorities in the Dutch East Indies, the 101st Naval Fuel Depot was established for the purpose of restoring such facilities speedily and effecting the greatest output in production. It was planned to send this unit to Dutch Borneo simultaneously

--33--

with the occupation of that area. As a large quantity of machinery was necessary and technical aid from commercial firms was required, it was especially difficult to maintain secrecy with this project.

Other Units

Preparation for the dispatch of fire-fighting units for oil fields, personnel for military post offices and weather units was undertaken simultaneously. No great difficulty was encountered with these units.

On 5 November 1941, the Chief of the Naval General Staff issued directives to all naval operational forces to commence defensive preparations in conformity with plans regarding their deployment. All surface units strove for the early completion of the planned emergency war preparations and all Naval Districts made efforts to intensify security patrols by organizing garrison units, comprised of members of the former naval barracks.

Progress of Armament and Other War Preparations at the Time of the Outbreak of War

Prior to the outbreak of war, successive supplementary armament and other war preparations had been undertaken and their completion had been accelerated to the utmost. The resultant progress in ship construction at the time of the outbreak of war on 8 December 1941 was generally as shown below. In addition, the Fourth Armament Replenishment Plan was almost completed and such preparations as the requisitioning and completion of converted vessels, strengthening of ground and port defenses, and procurement and

--31--

transportation of equipment and the necessary war materials were in progress.

Number of Ships at the Time of the Outbreak of War

Battleships

10

301,400 tons

Aircraft Carriers

10

152,970 tons

Heavy Cruisers

18

158,800 tons

Light Cruisers

20

98,855 tons

Destroyers

112

165,868 tons

Submarines

65

97,900 tons

Others

156

490,384 tons

Total

1,466,177 tons

Ships under construction

Battleships

2

128,000 tons

Aircraft Carriers

4

77,860 tons

Light Cruisers

4

42,700 tons

Destroyers

12

27,120 tons

Submarines

29

42,554 tons

Others

37

57,225 tons

Total

88

375,459 tons

Requisitioned Vessels

By the middle of 1940, the vessels requisitioned for the purpose, of continuing the China Incident amounted to 200,000 tons. At the end of 1940 it was decided to requisition an additional 1,650,000 ship tons and to continue to convert these vessels until the outbreak of war. At the time of the outbreak of war, the state of these vessels was:

Completely equipped converted vessels

522

approximately 1,150,000 tons

Converted vessels being equipped

41

approximately 170,000 tons

Vessels to be converted or equipped

180

approximately 290,000 tons

--35--

Requisitioned vessels which would not be converted

approximately 200,000 tons

Total

approximately 1,810,000 tons

Air Strength

Details of air strength at the time of the outbreak of war are shown on Chart 6.

Naval Personnel

The number of naval personnel at the time of the outbreak of war was as shown hereunder:

Active Service

Recalled

Reserve

Total

Officers

10,000

506

1,338

11,844

Special Duty Officers

2,997

775

3,772

Warrant Officers

5,262

3,415

8,677

Petty Officers and men

238,235

60,312

298,547

Total

65,008

1,338

322,840

The number of officers, according to their rank and branch of service, is shown on Chart 7.

--36--

Chart 6 — Air Strength at time of Outbreak of War

Details

Operational
Air
Group

Training
Air
Group

Shipborne

Total

Outer
Combat
Force

Inner
Combat
Force

O*

R*

O

R

O

R

O

R

O

R

Fighters

Interceptors

180

51

36

12

50

31

149

10

415

104

Night fighters

Carrier bombers

9

5

36

12

38

19

135

3

218

39

Carrier attack planes

6

2

42

14

165

189

9

402

108

Land reconnaissance planes

18

6

18

6

Land bombers

Land attack planes

255

84

80

20

4

2

339

106

Patrol planes

Transports

38

38

Fighter

2-seater reconnaissance seaplanes

10

4

28

14

24

12

99

12

161

41

3-seater reconnaissance seaplanes

16

7

28

16

40

20

74

11

158

54

Submarine reconnaissance planes

Flying boats

36

12

13

5

49

17

Land trainers

286

286

286

286

Sea plane trainers

94

94

94

94

Utility

84

84

84

84

Total

568

171

263

785

631

646

45

2262

940

O - Operational R - Reserve

--37--

Chart 7 — Roster of Naval Officers at Time of Outbreak of War

LINE

ENGINEER

PAYMASTER

MEDICAL

PHARMACY

SHIPBUILDING

ENGINE MANUFACTURING

ORDNANCE MANUFACTURING

TOTAL

TOTAL

Active

Recall

Reserve

Active

Recall

Reserve

Active

Recall

Active

Recall

Active

Active

Active

Active

Active

Recall

Reserve

Admiral

11

11

11

Vice-Admiral

62

4

3

3

2

1

1

72

4

76

Rear-Admiral

151

21

16

18

5

1

8

199

21

220

Captain

492

232

185

11

84

12

73

15

13

49

911

255

1,166

Commander

695

26

316

2

112

2

90

4

22

13

35

1,287

30

1,317

Lt Commander

720

33

12

338

4

112

2

208

27

7

19

13

52

1,469

66

12

1,547

Lieutenant

887

8

275

338

1

77

263

2

382

112

14

38

36

170

2,126

125

352

2,603

Lt (Jr Grade)

455

1

461

144

115

427

468

29

55

122

288

1,988

7

576

2,571

Ensign

636

240

157

158

62

45

8

14

49

244

1,215

398

1,613

Midshipman

440

96

47

6

30

101

720

720

Total

4,549

325

988

1,574

18

350

1,126

18

1,287

145

62

176

278

948

10,000

506

1,338

11,844

--39--

Chapter II

Outline of the fifth and Sixth Naval Armament Replenishment Plans

The Fifth Naval Armament Replenishment Plan was deliberated with the object of counteracting the Third Vinson Plan, but, in consideration of the huge scale of the Third Vinson Plan, and the fact that the United States had been adopting supplementary plans each year, calling for considerable strength, it was impossible for Japan, from the standpoint of her economic and industrial power, to establish a plan to counteract these plans. The Japanese Navy studied the situation carefully during 1940, and finally an understanding was reached between the Navy Ministry and the Navy General Staff around May 1941, to execute a plan starting from simple and prepared armament. At the same time, it was decided that, in regard to the budget, formal steps would be taken later. Details of the strength of vessels and air armament included in armament preparations requested in a preliminary discussion between the Navy Ministry and the Navy General Staff are shown in Chart 8.

The Navy Ministry studied these requests and decided that, in view of the budget, the materials on hand and the production facilities available, the plan for ship construction should be a 9-year plan starting in 1942 and ending in 1950. The necessary expenditure was estimated at ¥4,400,000,000 (¥4-$1). Although it was difficult to estimate the completion date of the air armament program, it was believed that it would require a shorter period

--41--

Chart 8 — Fifth Armament Replenishment Plan

Vessel strength requested

Battleships (Yamato-Class)

3

Super cruisers (new Type)

2

Aircraft carriers (Taiho Class)

3

Seaplane tenders

2

Flying boat tender (Large)

1

Flying boat tenders (Small)

6

Cruisers (Medium)

5

Cruisers (Light)

4

Submarine tenders

2

Minelayers

2

Netlayer

1

Destroyers (Class A)

16

Destroyers (Class B)

16

Submarines (Class A)

2

Submarines (Class B)

12

Submarines (Medium)

9

Submarines (Small)

9

Submarines (Navy Type large)

10

Submarines (Supply)

3

Gunboat (Large)

1

Gunboats (Small)

2

Escort ships (Class A)

4

Minesweepers

10

Subchasers

18

Light minelayers

8

Naval auxiliaries (Transport)

3

Naval auxiliary (Survey)

1

Naval auxiliary (Provision)

1

Naval auxiliary (Icebreaker)

1

Naval auxiliaries (Repair)

2

Total

159

650,000 tons

--42--

Chart 8 - Air strength requested (cont'd) Operational Air Group

Type of aircraft

Number of Units

Number of aircraft

Land fighters

14

336

Fighter-bombers

10

240

Land reconnaissance planes

2

48

Fighter seaplanes

12

288

Bomber seaplanes

2.5

40

Flying boats (Medium)

10

120

Flying boats (Large)

8

96

Patrol planes

6.5

104

Transports

2

48

Total

67 units

1,320

The grand total at the time of completion was 132 units.

Fifth Armament Replenishment Plan (Cont'd)

Training Air Group

Type of aircraft

Number of Units

Number of aircraft

Land trainers

10

240

Seaplane trainers

9.5

228

Utility trainers

21.5

516

Land combat planes (Small)

22.5

608

Combat seaplanes (Small)

11

198

Land combat planes (Medium)

10.5

252

Combat seaplanes (Medium)

8

96

Total

93

2,138

The grand total at the time of completion was 156 units.

--43--

of time than the ship program. The estimated amount required for the air armament program was ¥2,000,000,000.

As a tremendous amount of expansion would be required in both land and sea installations to cope with this program, ¥1,900, 000,000 was set aside for installations for increasing production capacity and ¥500,000,000 for training installations.

In order to achieve this objective, it was necessary for naval armament preparations to receive priorities in regard to securing personnel and materials, and the Army was asked to make concessions in this regard.

In accordance with the above, the Navy Ministry decided to convert two of the three Taiho-class aircraft carriers into Hiryu-class vessels and to support the over-all plan of the Navy General Staff.

In July 1941, just when various plans were gradually taking shape after the basic plan of the Fifth Armament Replenishment Plan was informally decided, the United States suddenly announced the Stark Plan, with its astronomical naval armament plans. This clearly demonstrated the United States' determination to dominate the seas. The plan was a great shock to the Japanese Navy and a quick counter-plan was sought. The Navy Ministry and the Navy General Staff conferred in regard to the over-all adjustment of the Fifth and Sixth Armament Replenishment Plans, and, toward the end of October, the Navy General Staff formally presented the Fifth and Sixth Armament Replenishment Plans simultaneously to the Navy Ministry. The Navy Ministry replied that utmost efforts would be

--44--

made for the execution of both plans in accordance with the decision to declare war, although nothing definite could be said about the Sixth Armament Replenishment Plan. In the meantime, air armament and the completion of 32 submarines of the Fifth Replenishment Plan would be undertaken, while other armament preparations contained in the same plan would be conducted after the budget of the following fiscal year was approved.

Immediately after the outbreak of the Pacific War, successive war preparation projects were undertaken. Japan was faced with a basic revision of the ratio between air and sea strength. Equipment of large ships called for in the ship plan was suspended and efforts were concentrated on small vessels and local strength. The Fifth Armament Replenishment Plan was first changed to the Revised Fifth Armament Replenishment Plan and later to the Third Stage Revised Armament Production Plan. The details of this revision are given in Monograph No 169, "Situation from Outbreak of War to Revised Fifth Armament Naval Armament Replenishment Plan."

The strength requested by the Navy General Staff of the Navy Ministry for the Sixth Armament Replenishment Plan was:

Ship strength: 197 vessels totaling approximately 800,000 tons, including 4 battleships, 4 super cruisers, 3 aircraft carriers, 12 cruisers, 34 destroyers and 67 submarines.

Air strength: 68 operational air groups (making a total of 200 groups after completion.)

Despite the fact that nothing definite was established in regard to such matters as the budget, because details of strength

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had not been decided, the Navy Ministry acknowledged the Sixth Armament Replenishment Plan. When war broke out, however, through battle experiences, a complete revision of plans for shipbuilding was brought about and the Sixth Armament Replenishment Plan ended as a mere paper plan.

As a condition of going to war, the Navy requested 1,450,000 tons of steel (including the priority allotment of secondary materials) and received an allotment of 1,100,000 tons as compared to the Army's 700,000 tons. This was tantamount to national priority being granted to naval armament preparation, and greatly contributed to the acceleration of naval armament in preparation for war.

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Japanese Monograph No. 169

OUTLINE OF NAVAL ARMAMENT AND PREPARATIONS FOR WAR

Part IV

PREPARED BY

MILITARY HISTORY SECTION

HEADQUARTERS, ARMY FORCES FAR EAST

DISTRIBUTED BY

OFFICE OF THE CHIEF OF MILITARY HISTORY

DEPARTMENT OF THE ARMY

FOREWORD

This is the fourth of a series of six monographs in regard to Japan's naval armament in preparation for and during the Pacific War.

Additional monographs covering Japan's naval armament plans are:

Mono No

Outline of Naval Armament and Preparations for War, Part I

145

Outline of Naval Armament and Preparations for War, Part II

149

Outline of Naval Armament and Preparations for War, Part III

160

Outline of Naval Armament and Preparations for War, Part V

172

Outline of Naval Armament and Preparations for War, Part VI

174

26 July 1952

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PREFACE

Through Instructions No. 126 to the Japanese Government, 12 October 1945, subject: Institution for War Records Investigation, steps were initiated to exploit military historical records and official reports of the Japanese War Ministry and Japanese General Staff. Upon dissolution of the War Ministry and the Japanese General Staff, and the transfer of their former functions to the Demobilization Bureau, research and compilation continued and developed into a series of historical monographs.

The paucity of original orders, plans and unit Journals, which are normally essential in the preparations of this type of record, most of which were lost or destroyed during field operations or bombing raids rendered the task of compilation most difficult; particularly distressing has been the complete lack of official strength reports, normal in AG or G3 records. However, while many of the important orders, plans and estimates have been reconstructed from memory and therefore are not textually identical with the originals, they are believed to be generally accurate and reliable.

Under the supervision of the Demobilization Bureau, the basic material contained in this monograph was compiled and written in Japanese by former officers, on duty in command and staff units within major units during the period of operations. Translation was effected through the facilities of Allied Translators

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and Interpreters Service, G2, General Headquarters, Far East Command.

This Japanese Operational Monograph was rewritten in English by the Japanese Research Division, Military History Section, General Headquarters, Far East Command and is based on the translation of the Japanese original. Editorial corrections were limited to those necessary for coherence and accuracy.

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TABLE OF CONTENTS

Page

Chapter I

Situation from Outbreak of War to Revised Fifth Naval Armament Replenishment Plan

1

General Situation

1

Air Armament

1

Combat Air Groups

2

Training Air Groups

3

Transport Planes

4

Shipborne Planes

5

Air Personnel

5

Emergency War Production Expediting Department

5

Battleship Construction Stipulated in Fourth Plan

7

Increase of Aircraft Carriers

13

Chapter II

Revision of Fifth Naval Armament Replenishment Plan (Revised Fifth Plan)

19

Progress of Revised Fifth Plan

20

Ship Strength

20

Air Strength

30

Supplementary Adjustments to Revised Fifth Plan

41

Supplementary Ship Construction Plan to Revised Fifth Plan

42

Appendix I

Naval General Staff Secret No 191

49

Appendix II

Official Reply from the Ministry of Navy: Secretariat Secret Document No 9599-2

51

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