Chapter 1: Japanese Naval Planning


This chapter outlines the Japanese Naval Planning for the Pacific War. The material was originally prepared by the Historical Research Department of the Japanese Naval Ministry, under the direction of Captain T. Ohmae, I.J.N., and consisted of answers to specific questions prepared by the Naval Analysis Division of the United States Strategic Bombing Survey. Further interrogations of Captain Ohmae and other Japanese naval officers were conducted in an effort to clarify specific points, and information obtained has been incorporated in the text.

The Naval Planning Organization

In describing the Japanese war planning organization, the peculiar nature of the Japanese Government must be kept continually in mind. In time of war the Japanese nation, militarily, economically, and politically was completely dominated by the military, the military being itself divided into two independent factions, the Army and the Navy. Although the idea that the Emperor was the supreme head and embodiment of the state was accepted by all, the precise extent of his authority and influence on national policy remained somewhat obscure. All actions, however, were taken in his name, and an Imperial Rescript, such as was issued on 14 August 1945, to terminate the war, had complete authority over the nation. Such being the case, it is important to note that the right of "access to the throne" was enjoyed only by the titular heads of the military services, the Chiefs of Staff of the Army and Navy and the War and Navy Ministers, and that the war powers of both Army and Navy were not subject to control by any other governmental body.

The Government (Cabinet) was dominated by the military in the persons of the War and Navy Ministers, both invariably from the active lists of the Army and Navy. Cabinets fell and were formed at the whim of the military; the resignation of either minister terminated a cabinet and failure of either branch of the services to nominate a minister prevented the formation of a new one.

An equally important point to be borne in mind is that the two factions of the all-powerful military, the Army and the Navy, exercised their authority only through mutual agreements. Unless an agreement was reached between these two factions, nothing could be accomplished.

The Imperial Headquarters, which was created only in time of war for the purpose of assuming supreme military command, was formed in November 1937. Its nucleus was the two general staffs, and it was headed by the Chiefs of Staff of the Army and Navy. As Commander in Chief of the Army and Navy, the Emperor was the titular head of this body, though the practical extent of his authority is not clear. What was discussed and agreed upon within this Headquarters was known only to the members. This headquarters was primarily concerned with operational plans, though being the supreme military command body it had great influence on national war policies. Within this headquarters Chief of the Army General Staff determined all matters concerning Army operations, and similarly the Chief of the Naval General Staff determined all matters concerning naval operations. Should there develop a difference of opinion between the two Chiefs, and should agreement not be reached, stalemate and inaction resulted.

The Government (Cabinet) was composed of the Prime Minister, the War and Navy Ministers, the Foreign minister and various other ministers. This body was primarily concerned with the economic and political administration of the nation and with the provision of the material and man power for the conduct of the war.


The Supreme War Council was the chief advisory body in formulation of war policies and was composed of members of the Board of Field Marshals and Admirals, the War and Navy Ministers, the Chiefs of Staff of the Army and Navy, and other high officers (including former War and Navy Ministers) appointed by the Emperor. The Imperial Headquarters however had more of a voice in formulating national policies than this unwieldy council. As a result of reverses, the Supreme War Council was superseded in August 1944 by the Supreme Council for the Direction of War. Although the Supreme War Council continued to exist, it retained little power. This Supreme Council for the Direction of War was established primarily to facilitate formulation of fundamental policies for the conduct of the war, and to obtain a national unity in the prosecution of the war. It was not concerned with operational plans, and acted chiefly as a liaison organization between the Imperial Headquarters and the Cabinet. It was composed of six voting regular members: the Prime Minister, the War and Navy Ministers, the Chiefs of Staff of the Army and Navy and the Foreign Minister. In addition, the regular members could bring any other minister to a meeting although these latter had no vote. The Deputy Chiefs of Staff also attended but did not vote. On occasion, and by Imperial Order, the President of the Privy Council would attend. When matters of special importance were to be discussed, the Emperor was requested to attend the meetings. There were also occasions when informal meetings were called by the Emperor; this occurred twice in June 1945 when attempts were being made to terminate the war.

During the later stages of the war liaison conferences were held every Tuesday and Friday at the Imperial Palace, but were not attended by the Emperor. Conferees were the Chiefs of Staff, their Deputies, the Chiefs of the 1st Sections (Plans), the Chiefs of the Operations Sections, and other senior officers of the Army and Navy General Staffs. Towards the end of the tenure of office of the Koiso cabinet, these conferences were attended by the prime Minister and the War and Navy ministers. At these conferences operational plans of the Army and Navy, and joint operations were discussed. However, no decisions were made.

Within the Naval General Staff, naval planning was accomplished in the First Section of the First Department, which section was concerned with operational planning. Logistic Planning was done in the Second Department, Naval Intelligence was provided by the Third Department, Communication Planning was done in the Fourth Department, and radio Intelligence was provided by a special section. Naval operations plans originated either in the First Department of the Naval General Staff or in the Headquarters of the Combined Fleet. After discussion by the Chief of the Naval General Staff and the Commander in Chief of the Combined Fleet, the final plans were drawn up. As previously mentioned these operational plans were discussed at the liaison conferences between the Army and Navy. Important plans were discussed at the Imperial General Headquarters and the agreement of the Army General Staff was obtained before the plan was submitted to the Chief of the Naval General staff. If the plan involved participation of the Government in providing necessary material and personnel, steps were taken to obtain the Navy Minister's agreement.

If the contemplated operations were of great importance, the directives were issued in the following manner: For those operations which extended beyond the authority delegated by Imperial Directive to the Chief of the Naval General Staff, the plan was submitted through the Imperial Headquarters to the Emperor for approval, after which it was issued as an order of the Naval Staff, Imperial Headquarters. Directives for plans of lesser importance which did not exceed that authority were issued in the name of the Chief of the Naval General Staff, but by direction of the Naval Staff, Imperial Headquarters.

The Basic Plan for the Greater East Asia War

The Basic Plan as formulated by the Japanese and placed into effect in December 1941, consisted of the following three phases:


By the successful accomplishment of the three phases of this plan the Japanese hoped to attain the goal of this war, making Japan self-sufficient.

Upon the successful completion of the first phase, and influenced by the unexpected ease with which their initial operations were carried out, the activation of the second phase was delayed and plans were formulated for further expansion.

These expansion plans were for the purpose of extending Japanese control of the Pacific and provided for the following:

  1. The capture of Port Moresby in order to strengthen the defenses of New Guinea and the Bismarcks.

  2. The capture of Midway in order to strengthen the defenses of the Central Pacific and to force a decisive engagement with the United States Fleet.

  3. The invasion of the Western Aleutians in order to reinforce the defenses of the Northern Area.

  4. The seizure of New Caledonia, Fiji and Samoa in order to cut lines of communication between the United States and Australia. This latter step was contingent on the successful completion of the others and was scheduled to be activated subsequent to the capture of Midway.

Upon completion of these expansion operations, the consolidation of position was to be completed as follows:

  1. The Northern Area, June 1942.

  2. The Solomons and Eastern New Guinea Area, November 1942.

  3. The Southern Areas, January 1943.

  4. General consolidation of all occupied areas, March 1943.

Supporting Plans

In support of the basic plan, plans were formulated for the conduct of the following operations:

  1. Raids on advanced Allied bases.-- These operations were for the purpose of preventing the strengthening of Allied positions as operational bases.

    1. Air raid on Port Darwin. This was carried out on 19 February 1942.

    2. Air raid on Ceylon. Raids by carrier forces were carried out on 4 and 13 April 1942.

    3. Air raids on Hawaii. These were to be conducted by seaplanes refueling from submarines at French Frigate Shoals and if possible by land based planes operating from Midway subsequent to its capture.

    4. Raids on Diego Suarez and Sidney by midget submarines. These were carried out on 31 May 1942.

    Every effort was to be made and every opportunity seized to reduce Allied air and surface strength by raiding tactics.


  1. Operations Against Allied Lines of Communication.-- The Japanese expected to accomplish much through the use of German submarine blockade tactics, and plans were made to employ such tactics in teh Pacific and Indian Oceans. Carrier and land based aircraft were to be employed whenever possible against lines of communication. They also planned to operate auxiliary cruisers in the Southern Pacific and East Indian oceans at the outbreak of the war.

  2. Operations for the Protection of Japanese Lines of Communication.-- Until about the end of 1942 shipping losses were comparatively light and no comprehensive plans for the protection of shipping were in effect. With the sudden rise in shipping losses the following countermeasures were taken to protect their lines of communications:

    1. Convoy operations were organized and a system of shipping control established.

    2. Surface escort units were organized and additional escort vessels provided.

    3. Antisubmarine patrols were activated and search and reconnaissance operations increased. A refuge policy for shipping was established.

    4. Small type vessels were employed for transportation in advanced areas.

    5. Development of improved antisubmarine weapons and the training of personnel in antisubmarine warfare were undertaken.

  3. Air Defense Operations in the Home Islands.-- Although this was an Army responsibility, the Japanese Navy acted in as assisting capacity. Air defense plans provided for the following:

    1. Employment of concentration in the use of intercept fighters.

    2. Installation of antiaircraft batteries in the vicinity of metropolitan and industrial areas.

    3. Installation of radar at strategic points.

    4. Stationing of patrol vessels to the east and south of the Home Islands.

    5. Improvement of fighter performance; research toward development of improved types.

    6. Measures for the dispersal and removal to underground installations of industrial activities, and the evacuation of industrial areas.

    7. Strenghtening of air defense organizations.

Japanese Comments on the Basic Plan

In commenting on the Basic Plan and upon the implementation of this plan the Japanese made the following comments and expressions of opinions. Several of the senior Naval officers interrogated stated that even the original perimeter was perhaps too extended to be maintained with the military potential available. They further felt that they failed properly to estimate their military and economic requirements for the war, and that they had particularly underestimated the economic potential of the United States and the United States will to fight.

The unexpected success of the operations in the first phase, and the ease with which these oprations were carried out, caused the Japanese to underestimate the existing United States strength and to embark on a further expansion. This policy of further expansion was hotly debated; however the faction in favor of pushing the initial advantages won out. The air raid on Tokyo on 18 April 1942 had some influence on this decision in that it tended to confirm the need for additional bases to the east. As they stated, the reserve strength which should have been used in consolidating the positions seized in the initial phase was dissipated in the unsuccessful attempts at further expansion. In view of the limitations of Japnese miltiary strength, shipping, and the national economy, this attempt to expand an already too big strategic sphere brought about unsolvable problems. At the time when the defenses of those areas which had to be held at any cost were left wanting, operations for the capture of port Moresby, Midway, and the Aleutinas were undertaken, thereby further dissipating the nation's strength. Thus it was conceded that the expansion program which was intended to strengthen the Japanese defense position actually weakened it. All the


Japanese interrogated on this subject considered that this expansion was a fundamental error in the conduct of the war.

The losses sustained in these unsuccessful attempts at expansion beyond the original outlined perimeter proved to be the greatest handicap in carrying out subsequent naval operations. It was stated that the loss of a major portion of their carriers in these operations was a serious blow to their naval air strength and, after still further air losses during the Solomons Campaign, the Japanese Naval Air Force never fully recovered.

When the Japanese were forced to return to their original plan of consolidation, it was with greatly reduced strength. Although priority was given to the construction of carriers and the strengthening of their air forces, they stated that they were unable to match the speed of the United States counteroffensives, and that they were continually behind schedule in the building up of defenses and the training of their air forces.

Comments on Supporting Plans, Their Concept and Execution

Japanese opinions regarding the concept and execution of supporting plans obtained in interrogations are summarized below.

  1. Raids on advanced Allied bases.-- As could be expected from their military ideology of the offense, the Japanese considered that operations of this nature would be of great value and gave them high priority. In the early stages of the war, these raids were quite successful, particularly those carried out by carrier forces.

    After the Battle of Midway, in which the Japanese carrier forces sustained such heavy losses, most of the strength which they could muster had to be used in the attempts to counter United States offensive operations. Thus after the early raids, Japanese carrier forces were unable to continue these operations against Allied bases. With their carrier forces reduced to relative impotence, the Japanese attempted with small success to conduct raids using land-based air forces. United States opposition increased at every point while the training and quality of Japanese air forces declined steadily. Toward the end of the war, the chief Japanese hope seemed to lie in raids against United States advanced bases by special attack (Kamikaze) forces. Such raids on anchorages were carried out by submarine-borne "human torpedoes" in early 1945, and by a special attack force of airplanes on Ulithi in March 1945. Again they were not considered highly successful, although abortive attempts were made to repeat the latter.

    The Japanese in analyzing these raiding tactics, felt that they started too late to originate and to prepare and train for that type of operation -- the use of suicide tactics of all types. They continue to feel that, had adequate advance preparations been made and the inherent spirit of the special suicide attack been fully utilized, these tactics perhaps would have reversed the tide of battle.

  2. Operations against Allied Lines of sea communications.-- Although some results were obtained from the outbreak of the war until about the time of the Guadalcanal battles, submarines, which would have been the greatest threat to our sea communications, were largely employed in the defense of vital areas, in supply operations to bypassed bases, and in tactical support of fleet operations. Hence only a small force of submarines was employed against Allied shipping, and due to the effectiveness of the United States antisubmarine measures these operations were confined to such areas as the Indian ocean.

    As regards surface raiders, very little preparation and training was carried out before the war and the results obtained by these forces were very slight.

  3. Operations for the protection of Japanese line of communications.-- They Japanese were quite frank in condemning their failure to protect their lines of communications. They felt that as a whole their military ideology placed too much emphasis on offensive operations, leaving much to be desired


    in the study and planning for such purely defensive operations as protection of surface shipping. Moreover since shipping losses were comparatively light during the first year of the war, no consideration was given to developing and improving tactics for this type of operation. Therefore, by the time that losses took an alarming aspect, the Japanese were behind in the development of countermeasures and continued to fall farther behind as the attacks against shipping were accelerated. In retrospect they felt that, since the basic objective of the war was to obtain for Japan the resources in the southern area, maintaining the security of the sea lanes between these resources and the industrial homeland should have been considered an integral part of the basic war plans. Inability to maintain the security of these sea lanes had a vital effect on her ability to sustain her war industries.

  1. Air defense operations in the Home Islands.-- By the time air attacks began against the home islands, the Japanese fighter defense was inadequate to meet these attacks. As a result of losses sustained in prior operations and the continuing attrition, the defense was inadequate in both numbers and performance. Although attempts to obtain improved types were made, the planes did not materialize.

    As a result of heavy losses suffered in combat prior to the threat of major air attacks on her homeland, a large part of her effective fighter strength had been destroyed. Lack of aviation gasoline and the need for conserving their remaining strength for the defense against invasion, resulted in orders to disperse or conserve the remaining fighter strength.

    The dispersal and moving underground of essential industries, as well as the evacuation of the metropolitan areas, were not effected until it was too late.

Operational Plans Formulated Throughout the War

After the failures at Port Moresby and Midway in May and June 1942 Japan attempted to consolidate the occupied areas in accordance with the original basic plan. Defenses in general were to be strengthened in the Western Aleutians, Ogasawara, Wake, Marsh, Gilberts, Bismarcks, New Guinea, and the entire southern occupied area. The areas to be held at all costs were the Southern Resources Area, and the area to the westward of a line joining the Kuriles, Marianas, and Carolines. In March 1943, in view of the unfavorable outlook in the Solomons and Eastern New Guinea, these areas were removed from the vital area and only delaying operations were to be undertaken there.

Operational plans for defending the vital areas and the defensive perimeter were prepared. The objective of these plans was to defend these areas, to destroy United States forces which attempted to attack the defense perimeter, to cut United States lines of communication, and to establish a strategically strong position. In support of these plans every effort was to be made to build up naval air forces, both carrier and land-based.

In order to achieve this purpose, the following operational tasks were to be performed:

  1. Establishment of a strategically strong position based on air power.

  2. Destruction of the United States Fleet based in advanced positions or after enticing it into action under conditions favorable to the Japanese; invasion and destruction of positions which were strategically important, thus forcing abandonment of any offensive operations before they could be activated.

  3. Swift consolidation of secured areas, so that any attempt to counterattack could be repulsed through close cooperation between air and sea power.

  4. Increase in commerce raiding operations so as to prevent reinforcement in men and supplies.

  5. Increase in protection of the Japanese lines of communication.

In accordance with the foregoing, and in cooperation with the Army, a speedy strengthening of defenses was attempted. However the carrying out of this task was beyond Japanese capabilities.

The "Z" Operation Plan (formulated about May 1943)


The operational policy of this plan was:

  1. To establish a front line of defense along the line joining the Aleutians, Wake, Marshalls, Gilberts, Nauru, Ocean, and the Bismarcks, and to strengthen the principle positions along this defense line, with local commanders responsible for countermeasures against any attacks against this line. The Combined Fleet was to stand by in the vicinity of Truk.

  2. In the event of attack, to draw the attacking force toward the principle positions and to destroy it by the joint action of land-based air and mobile attack tactics of the carrier striking force.

  3. To conduct raids against United States carriers in order to reduce their power.

The tasks to be performed were as follows:

  1. Maintenance of a strict watch on the main strength of the United States Fleet by submarine reconnaissance.

  2. Search and reconnaissance by land-based aircraft.

  3. Reduction of enemy strength by destructive raiding of advanced enemy bases.

  4. Upon receipt of reports of contact with enemy forces, the Mobile Fleet was to sortie without delay and, operating in close cooperation with land-based air and submarine forces, destroy first the enemy carriers and, second, the transports.

  5. Garrison forces at the point of enemy attack were to endeavor to destroy the enemy at the shore line. If, however, the enemy succeeded in forcing a landing, local forces were to counterattack persistently in an effort to delay the enemy as long as possible and to prevent the establishment of bases.

  • Naval Surface Forces

    1. In the Truk-Marshalls-Gilberts area: local naval forces of the 4th Fleet consisting of Cruiser Division 14 and several destroyers.

    2. In the Bismarck-Solomons area: local naval forces of the 8th Fleet consisting of Destroyer Squadron 3.

    3. At Truk: main strength of the Combined Fleet consisting of Battleship Division 1; Cruiser Divisions 4, 5, 7, and 8; Carrier Division 3 (Air Flotillas 1 and 2); Destroyer Squadrons 2 and 4; and Submarine Squadrons 1 and 3.

  • Naval Air Forces

    1. In the Marshalls area: Air Flotilla 22.

    2. In the Truk-Bismarcks-Solomons area: 11th Air Fleet consisting of Air Flotillas 25 and 26, plus two Air Groups.

    As a result of the Munda and Kolombangara landings and the landings at Lae and Salamaua, it became apparent that Rabaul could no longer be considered an effective position. Therefore, at the end of September 1943, the defense line was withdrawn and the vital area was reduced to that within the line Kuriles-Marianas-Carolines, and the Sumatra-Java-Timor line. Efforts were then concentrated on the strengthening of these areas and on sending reinforcements. But due to the lack of shipping the desired results were not achieved.

    The United States occupation of the Gilberts and Marshalls was resisted with only inadequate land-based air and local garrisons. As these areas had been removed from the vital area in September 1943, the Combined Fleet was not committed. A further reason for not committing the fleet was that, as a result heavy losses sustained by the carrier air groups at Midway and in the Solomons, the carrier divisions were not ready for operations. The "Z" plan, in modified form, remained in effect until May 1944, when it was cancelled and superseded by the "A" plans.


    The "Y" Operations Plan (formulated about May 1943)

    The operational policy and tasks for this plan were similar to those for the contemporary "Z" Plan, except for the area of operations. The front line of defense prescribed in this plan was that joining the Andamans, Nicobar, Sumatra, Java, and Timor. In case this defense line alone was threatened, the main strength of the Combined Fleet was to be moved to the Philippines or to Singapore. In case this defense line was threatened and the "Z" Plan also activated, then only a portion of the carrier force was to be utilized, together with local forces available.

    The position of forces prescribed by this plan was:

    1. Naval Surface Forces -- There were available only minor units in small numbers as local naval forces in this area. These were attached to the Southwest Area Fleet at Singapore, and to the 2d, 3d, and 4th Southern Expeditionary Fleets at Surabaya, Manila, and Amboina respectively.

    2. Naval Air Forces -- The main strength of Air Flotilla 23 was in the Celebes area; the remainder was in Manila and Northern Sumatra. After September 1943, the 13th Air Fleet (Air Flotillas 23 and 28) was similarly deployed.

    The "A" Operations Plan (formulated May 1944)

    At the end of February 1944, the Gilberts and Marshalls had been occupied and Truk and the Bismarcks neutralized and bypassed. The outer defense was then further withdrawn to the Marianas, Palau, and the Sumatra-Java-Timor-Western New Guinea line. The "A" plan was drawn up for a decisive action in defense of this line. Force necessary for this operation were expected to be ready the latter part of May 1944.

    The objective of this plan was to concentrate all available forces for a decisive action against United States attack forces.

    The tasks to be performed were as follows:

    1. Consolidation of decisive battle forces was to be expedited. The enemy fleet's main force was to be contacted and destroyed sometime subsequent to the latter part of May, in the general area between the Central Pacific and the Philippines, or in the area south of the Timor-Java-Sumatra line. Unless otherwise directed, participation in any decisive action prior to the time when the forces could be thoroughly organized was to be avoided. Insofar as possible, the seas close to the bases where the Mobile Fleet was based were to be selected as the scene for the decisive battle.

    2. In the event that the enemy's attack materialized prior to the time of completion of the organization of the Mobile Fleet, decisive action employing naval surface forces was to be avoided and land-based air and local defense forces would be employed in intercepting and destroying the attacking force. In this eventuality every effort was to be made to avoid excessive losses of shore-based air, except where such losses would have a favorable effect on the ensuing decisive action.

    3. At the opportune moment when preparations for the decisive action had been completed, the entire force was to be thrown against the enemy's main strength in an effort to contact and destroy it.

    4. In preparation for the decisive action, priority was to be given to preparations for air operations by construction of air bases and by stockpiling of fuel and ammunition. The Army and Navy were to cooperate in these preparations, and share all air bases jointly.

    The disposition of forces prescribed by this plan was:

    1. Naval Surface Forces: The forces of the First Mobile Fleet, consisting of Battleship Division 1 and 3, Carrier Divisions 1, 2, and 3, Cruiser Divisions 4, 5, and 7, and Destroyer Squadrons 2 and 10, were to stand by in the Central and Southern Philippines.


    1. Naval Air Forces: The First Air Fleet, consisting of Air Flotillas 61 and 62, was to be deployed in the Central Pacific (Marianas-Western Carolines), Philippines, and the area north of Australia.

    The preparations for the decisive action under this plan were never completed as planned and the training of the air force, particularly the carrier air groups, was behind schedule. The Japanese considered that the carrier air groups would be ready in August. In view of the United States carrier strike on Palau in the latter part of March 1944, and the occupation of Hollandia in April, the Japanese estimated that the next attack would be against Palau, which also was a scene of action favorable to their plan.

    However, when United States forces appeared off Saipan in June and initiated their assault the "A" plan was activated even though complete preparations had not been realized. In the ensuing battle of the Philippine Sea, the major portion of their carriers and practically all of the carrier air groups were lost. In addition the shore-based First Air Fleet suffered severe losses. These losses to the Japanese Naval Air Force vitally affected all subsequent operations, and the prospect of success in future operations at sea became very dim.

    The "Sho" Operations Plan (formulated in July 1944)

    After the fall of the Marianas, and as a result of the heavy losses sustained in that campaign, the Japanese considered that any attempt to recapture these islands was out of the question. The United States had obtained control of the Central Pacific areas. This again forced the Japanese to further withdraw their defense line to one running from the Home Islands through the Nansei Shoto, Formosa, Philippines, and Timor-Java-Sumatra. The "Sho" plan was drawn up for a decisive action in defense of this line, with the probability that it would take place in the vicinity of the Home Islands, Nansei Shoto, Formosa or Philippines. The Nanpo Shoto was also considered as a possible scene of action. The next attack was expected some time after August 1944.

    The operational policy of this plan was:

    1. By means of an all-out coordinated effort of land, sea, and air forces, to fight a decisive action in defense of the Home Islands, Nansei Shoto, Formosa, and Philippine areas. Only under favorable conditions would a decisive action be fought in defense of the Nanpo Shoto.

    In accordance with the estimate of the probable areas of action, and in order to facilitate preparations and to establish command relationships the following four plans were drawn up:

    As the Sho Number and 1 and Number 2 were considered most likely to be activated, priority was given to strengthening the defenses in these areas. After a brisk discussion between the Army and Navy, it was agreed that an all-out land defense would be made only if the action were to occur in the Northern Philippines. If the action were to occur in the central or southern part, only air and surface forces would seek decisive action.

    The tasks to be performed were:

    1. Destruction of enemy forces at the point of attack, by air, sea, and land forces concentrating on carriers and transports. The primary target fo the Naval air forces was to be the United States Carrier Task Force; for Army air forces, the convoys.

    2. Disposition of air strength in depth, and conservation of this strength until just before the attempt to land.


    1. All-out air attacks and surface torpedo attacks when the enemy fleet and convoys approached sufficiently close to the objective.

    2. Maintenance of a counter landing force in readiness; to counter landing if a favorable opportunity occurs.

    The initial disposition of forces prescribed by this plan:

    1. Naval Surface Forces

      1. Inland Sea area: The 3d Fleet, consisting of Carrier Divisions 1, 3 and 4, and Destroyer Squadrons 10 and 11; the 6th Fleet consisting of Submarine Squadrons 7, 8, and 11, plus Battleship Division 2 of the 2d Fleet.

      2. Ominato area: The 5th Fleet consisting of Cruiser Division 21 and Destroyer Squadron 1.

      3. Philippines area: Southwest Area Fleet consisting of Cruiser Division 16 plus some destroyers.

      4. Singapore area: The 2d Fleet consisting of Battleship Divisions 1 and 3, Cruiser Divisions 4, 5, and 7, and Destroyer Squadron 2, plus one half of Destroyer Squadron 10.

    2. Army and Navy Air Forces

      1. Northeast and Home Islands area: Army, the 1st, 10th, 11th, and 12th Air Divisions plus Training Command Aircraft; Navy, the 3d and 12th Air Fleets plus Air Groups of the 3d Fleet.

      2. Nansei Shoto-Formosa areas: The Army 8th Air Division and the Navy 2d Air Fleet (this air fleet was later sent to the Philippines).

      3. Philippines-Area North of Australia: The Army 4th Air Army and the Navy 1st Air Fleet.

    Palau and Morotai were attacked in September, the Japanese estimated that the next move would be against the Philippines so no changes were made in the "Sho" plan. When in October the attacks did occur on the Central Philippines, the "Sho" plan was activated and, in accordance therewith, the Fleet was committed and reinforcements were dispatched to Leyte.

    The Battle for Leyte Gulf was a complete defeat for the Japanese Fleet. In it the major portion of the remaining Japanese naval surface strength was destroyed. In addition the Army and Navy air forces in the Philippines suffered severe losses. This campaign also saw the initiation of special attack (Kamikaze) tactics.

    The "Ten" Operation Plan (formulated in early March 1945)

    With the occupation of the Central Philippines and the establishment of United States air bases in this area, the final severance of lines of communication between Japan and her vital resources was accomplished. The Japanese estimated that United States strategic plans were aimed at positions surrounding the China Sea, with the most probable objective being in the Nansei Shoto. With operations continuing throughout the Philippines, the Japanese did not expect that Formosa would be attacked. The "Ten" plan was formulated for the final defense of an inner line established through the Home Islands, the Nansei Shoto, Formosa and the South coast of China. With the Japanese fleet almost completely destroyed and the air force reduced to the employment of suicide tactics, a "decisive action" was no longer possible and only a "last ditch" defense was contemplated.

    The operational policy for this plan was:

    1. To hold out in the Nansei Shoto, Formosa and Shanghai areas.

    2. In the event a hopeless situation arose, to make the enemy losses as heavy as possible and to delay the development of air bases to the utmost.


    1. During this period further preparations were to be made for the final defense of the Home Islands.

    In order to facilitate defense preparations in the probable objective areas, and to establish command relationships, the following four plans were drawn up:

    The tasks to be performed were:

    1. To combine and concentrate the major portion of Army and Navy air strength, and to deploy these forces in the Kyushu-Nansei Shoto area.

    2. To use the major portion of this combined air strength in special attack (Kamikaze) tactics.

    3. To meet the attacking forces with the entire strength of the aerial special attack force with the object of destroying it. The Naval air force was to consider the destruction of enemy carriers as the primary objective.

    4. When favorable opportunities arose, the use of surface forces was to be considered.

    5. No preparations were to be made for the training of surface counter landing forces.

    The disposition of forces prescribed by this plan was:

    1. Naval Surface Forces: Only remnants of the Combined Fleet remained in the Inland Sea consisting of Battleship Divisions 1 and 3, Carrier Division 1 and 4, three destroyer squadrons, about 30 submarines, and a few cruisers. Most units were under repair. No trained air groups were available for carriers.

    2. Air Forces:

      1. Home Islands area (including Nansei Shoto): Army, 6th Air Army; Navy 3d, 5th and 10 Air Fleets.

      2. Formosa: Army, 8th Air Division; Navy, 1st Air Fleet.

      3. Southwest Area: Army, 3d Air Army; Navy, 13th Air Fleet.

      4. China: 5th Air Army.

    In accordance with plans Iwo Jima was defended only by limited operations of naval land-based air forces. However the United States amphibious assault on Okinawa was opposed by large-scale suicide attacks and a desperate suicide sortie by the battleship Yamato with an escort of light vessels. Heavy losses were suffered by the remnants of the Japanese Army and Navy Air Forces.

    The "Ketsu" Operation Plan (formulated at the end of March, 1945)

    With the fall of Iwo Jima and Okinawa, the last line of defense was broken; the air and sea blockade of the Home Islands was complete. The next projected advance of the United States forces was obviously the invasion of the Home Islands with the Southern Kyushu and the Kanto area the most probable objectives. The "Ketsu" plan was drawn up for the final defense of the Empire.

    The operational policy for this plan was:

    1. To use the concentrated strength of all forces in an effort to smash the advancing United States forces. Strong, quick, and decisive operations were to be carried out to the bitter end.

    2. To make every effort to strengthen the defenses of the vital areas.

    The tasks to be performed were:

    1. Strengthening of vital invasion points, and important straits and bay entrances. Steps were taken to guarantee security of surface communications.


    1. Mobilization and concentration of all mobile forces, particularly air and suicide attack strength, in order that enemy forces could be successfully counterattack while enroute to invasion points.

    2. To conduct all types of suicide attacks against enemy convoys, both at sea and when close to land.

    3. In anticipation of large-scale air raids, to take every possible measure to preserve and increase combat strength. Strong measures were to be taken to make appropriate disposition of military supplies and to expedite dispersal and evacuation of establishments.

    4. Every means was to be employed to give full play to the united combat strength of the Army and Navy air arms. The Army and Navy air forces were to make joint use of bases, and maintenance and logistic supplies were to be interchanged.

    5. Prior to activation of these plans, antiair and antisubmarine operations were to be accelerated.

    6. Raids with the object of neutralizing enemy air bases in the Marianas, Iwo Jima, and Okinawa were to be carried out.

    The disposition of forces was:

    1. Naval Surface Forces: All remaining naval surface forces were scattered among bases in home waters, the major portion being at Kure. Except for personnel of AA guns, most of the personnel has been assigned to various types of suicide operations.

    2. Air Forces: All the remaining air strength of the Army and Navy, including training planes, was assigned for an all-out defense against invasion. The greater proportion of these planes were suicide planes. The Army Air Force, consisting of the 1st, 5th and 6th Air Armies, had approximately 3,200 planes of all types. The Navy Air Fleets with various Air Flotillas, could muster approximately 5,200 planes of all types. These planes were disposed throughout all the Home Islands and in Korea and China.

    Preparations for these operations were considerably disorganized by increasingly heavy United States raids by land-based and carrier-based planes. Attacks preliminary to the invasion were being systematically conducted against all of the Home Island by Allied carrier forces. These attacks included shore bombardment by heavy ships and shipping sweeps of coastal waters by light surface forces.

    The Imperial Rescript of 14 August 1945 terminated hostilities, and on 2 September 1945 the surrender terms were executed.


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