SRH—149
A
Brief History of
Communications
Intelligence
in
the United States
by
Laurance F. Safford
Captain, United States Navy
(Retired)
DECLASSIFIED per Sec. 3, E. 0. 12065
by Director, NSA/Chief, CSS
6 March 1982.
REVIEWER'S
NOTE:
This document, designated SRH‑149 in the
records of the National Archives, Washington, D.C., was prepared 21‑27
March, 1952, by Captain Laurance F. Safford, United States Navy with special
reference to coordination and cooperation and access to various historical
records, with the objective of bringing diverse documents into a usable
narrative history of a Naval activity. The document does not constitute an
official Navy history, and no claims are made regarding its completeness or
accuracy. On 6 March 1982 it was further certified to be declassified by the
Director, National Security Agency.
2
SRH‑149
A Brief History of
Communications Intelligence in the United States
Prior to 1917, United States activity in the field
of Communications Intelligence* was sporadic, and there is little recorded of
it. For all practical purposes, the history of American cryptanalysis began
with the entry of the United States into World War I. Codes and ciphers at that
time, even those used to carry the most sensitive information, were by current
standards naive. They were hand‑coded and hand‑applied cipher
systems usually overlying double‑entry code books, the attack upon which
required skills and patience but not the elaborate electronic and tabulating
devices of today. Consequently, the codes which this government
"cracked" from 1917 to 1919 were handled by a small group of
lexicographers, mathematicians, and people who had acquired some background in
what was then the hobby of cipher construction, usually related to some such
cult as the "Baconian Theory."
The War Department set up the first organized cryptanalytic office in
June 1917, under Mr. H. O. Yardley, an ex‑State Department telegrapher
who had taken some interest in cryptography, or cipher construction. The
strength of this office, at first three people, grew rapidly. At the conclusion
of the War it was subdivided into functional sections and had a table of
organization of some 150 persons with an annual budget of $100,000. Its
security regulations were primitive. Ciphers were broken and code values were
recovered using hand methods. The volume of traffic handled by the group was
nevertheless respectable, and the results of their work on the military,
diplomatic and economic fronts were important enough to impress both the
General Staff
* The phrase "communications intelligence," abbreviated for the sake of convenience to "COMINT," means intelligence produced by the study of foreign communications, including the breaking, reading and evaluating enciphered communications. "Cryptology" is a synthetic term which is applied to two cipher activities, the construction of ciphers and the breaking of ciphers. In turn, these two activities are termed "cryptography" and "cryptanalysis."
4
and G‑2. But its budget for fiscal year 1921
ran into opposition, and during the decade was steadily reduced each year,
falling at length to $25,000. No research was carried on. There were no
training activities, no intercept, no direction finding studies. The personnel
fell to six. The coup-de-grâce came in 1929, a few weeks after Mr. Stimson
became Secretary of State. By default, the records and physical possessions of
H. O. Yardley's "American Black Chamber" fell to the Signal Corps of
the Army.
The Navy Department
attempted no cryptanalytic work during 1917‑18. But it did set up a
system of medium frequency direction finder stations along the Atlantic Coast
for tracking German submarines operating in the Western Atlantic. After the
Armistice, these Navy coastal D/F stations were diverted to use as aids to
navigation and were retained in full operation until the "navigational D/F
service" was turned over to the Coast Guard in 1941. Although the U.S. led
the world in the development and use of medium‑frequency direction
finding, it lagged badly in development of high‑frequency direction
finding (HF D/F).
Finally, in 1937‑38,
the Naval Research Laboratory developed a HF D/F system that would work.
Production was undertaken at the Naval Gun Factory. Installations were then
made at selected coastal D/F stations in the continental U.S., and overseas
"strategic" (HF) D/F stations were established at Manila, Guam,
Midway, Oahu, Dutch Harbor, Samoa, Canal Zone, San Juan, and Greenland. By 1939,
the "strategic" D/F organization was successfully tracking Japanese
warships and merchant vessels in the Western Pacific.* By 1940 the East Coast
strategic D/F net was likewise locating and tracking German submarines in the
Atlantic. About May 1941 the Navy Department and British Admiralty began
exchanging D/F bearings on German U‑boats. U.S. D/F stations compared
favorably with British D/F stations in this respect. These U.S. Navy D/F
bearings were also supplied to all Naval Air Stations for air navigation and
lost plane procedures, and were also made available to the FCC and to the Army.
In 1940 Monsieur Busignies
fled to America from Paris, ahead of the advancing German armies, taking with
him complete plans for a new and radically superior fixed‑Adcock type of
HF D/F system. The Navy placed a production contract for the Busignies D/F
through the Federal Telephone and Telegraph Company. It was necessary to re‑engineer
the Busignies D/F to take standard American tubes, 60‑cycle power supply,
and otherwise adapt
* In contrast, the Japanese had been tracking U.S. Naval
ships since 1934.
5
it to American use and manufacturing processes. As a
result, the Busignies D/F did not get into service until 1943.
The Collins Radio Company
submitted to the Navy plans of a new and radically different type of rotating
D/F system about the same time as Monsieur Busignies. The Collins D/F was
rushed into production and went into service in 1942. On 7 December 1941, the
U.S. Navy was using the DT‑1 and DT‑2 HF D/Fs of Navy design and
construction, and thus had a continuity of direction finding effort since 1917.
On the Security side, the
Navy built up during 1917 and 1918 an integrated organization (the Code and
Signal Section of Naval Communications) for the compilation, production,
distribution and accounting of Codes and Ciphers. The Registered Publication
Section was divorced from the Code and Signal Section in 1923 and its functions
were expanded to include distribution and accounting for all secret and
confidential documents prepared by the Navy Department and bearing a register
number.
During 1917‑18, the
U.S. Navy relied heavily on cryptographic advice given by the British
Admiralty, whose famous "Room 40" led the world in practical
cryptanalysis at that time. The Code and Signal Section, maintained at reduced
strength after the Armistice, gradually built up a War‑Reserve of Naval
Codes and Ciphers and made plans for technical improvements. As early as 1922
the Navy recognized that the future of secret communications lay in machine
cipher systems rather than in the then‑current systems of enciphered‑codes.
The Navy, therefore, sponsored the development of the Electric Cipher Machine
(ECM) from that time on. By 1931 the Navy had tested and discarded the
double-printer model of the Hebern Cipher Machine and had placed an order for
30 single-printer Hebern Cipher Machines for service tests. An early form of
"strip cipher" was introduced by the Navy as a step in the transition
from codes to ciphers and was to serve as an interim system until the Electric
Cipher Machine could be perfected. The Army took a dim view of the Electric
Cipher Machine and attempted to induce the Navy to abandon it. Under the
circumstances, "collaboration" with the Army was difficult.
In 1924 the Navy established
a Communication Intelligence Organization under the Code and Signal Section of
the Office of Naval Communications with the covering title of "Research
Desk." The initial allowance was one officer and four civilians, later
supplemented by two enlisted radiomen. An immediate start was made on
establishing intercept stations in the Pacific Area, which permitted the Navy's
Cryptanalytic Unit to function, training
6
personnel, and planning for future expansion.
Training was accomplished through technical manuals (which had to be prepared)
and correspondence methods plus temporary duty "under instruction" in
Washington. Intercept stations were established as trained personnel became
available in approximately the following order: Shanghai, Oahu, Peking, Guam,
Manila, Bar Harbor (Maine), Astoria (Oregon), and Washington, D.C. Minor
intercept activities were later established at various "strategic"
(HF) D/F stations. Advanced Communications Intelligence (decrypting) Units were
established in the Manila Area in 1932 and at Pearl Harbor in 1936, serving
CINCAF and CINCPAC respectively.
Beginning in 1935, selected
Naval Reserve Officers were ordered to Washington, normally for a two-week
"training cruise," where they were given advanced cryptanalytical
instruction and training. In 1938 the "Communications Security Group"
(successor to the "Research Desk") took over the operation of all
Naval D/F facilities. The growth of the Navy COMINT Organization was slow,
steady, and uninterrupted until the fall of France (June 1940). The
proclamation of the Unlimited National Emergency (June 1941) permitted calling
to active duty trained (or at least partially trained) Naval Reservists
previously earmarked for communications intelligence duty. The strength and
growth of the Navy COMINT Organization is shown by the following table.
Complement of the Navy
Communication Intelligence Organization |
|||||
|
|
|
|
|
|
Date |
Officers |
Enlisted |
Civilians |
Total |
|
1925 |
1 |
2 |
4 |
7 |
|
1926‑1935 |
Net increase of about 10
men per year, plus "qualified" personnel performing other duties. |
||||
1936 |
11 |
88 |
10 |
109 |
|
June
1940 |
12 |
121 |
15 |
147 |
|
|
(Does not include 150
operators performing navigational DIF services.) |
||||
January 1941 |
44 |
489 |
10 |
543 |
|
7 December 1941 |
75 |
645 |
10 |
730 |
|
Once Intercept Stations had
been established at Shanghai and Oahu, with a few radio operators having
learned how to copy the Japanese Morse Code, the U.S. Navy was off to a flying
start in its study of Japanese Naval Messages. Due to a fortuitous
circumstance, about 1922 a shock-team of FBI, ONI, and New York Police
representatives succeeded in "picking-the-lock" of
7
the safe of the Japanese Consul General in New York,
where they discovered a Japanese Naval Code belonging to a Japanese naval
inspector. Over a period of time this code was photographed, page-by-page, and
re-photographed a year or two later to pick up extensive printed changes. The
cipher used with this code was not too difficult and we were literally
surfeited with blessings.
The one or two available
Japanese translators could not possible go through all the intercepted
messages, so it was necessary to sort out the high priorities, important
originators, important addressees, etc., and thus skim off the cream. The
Japanese used the same code until December 1930, thus giving U.S. Naval
Authorities (CNO, War Plans, and Naval Intelligence) a complete picture of the
Grand (Japanese Naval) Maneuvers of 1930 including Japanese Naval War Plans,
strategic concepts, and the fact that the maneuvers were a "cover"
for a hundred percent mobilization of the entire Japanese Navy. When the
Japanese Army began the invasion of Manchuria a few months later, its rear was
guarded by Naval Forces superior in strength to the peace-time U.S. Navy, and
the Chief of Naval Operations knew it.
In the Army, meanwhile, the
period 1930 to 1935 was one of energetic revival. In these years the work was
under the direction of Mr. William F. Friedman, who has continued to be a
leader in the field and who is presently associated with AFSA, the joint
Army-Navy-Air Force cryptologic center in Washington. His first job was to
assemble personnel and enlist new recruits. A training program with
instructional literature was organized, and it is noteworthy that for the first
time a total cryptologic activity (the construction of our own ciphers) was
envisaged. There was still no Army intercept service as we understand it today,
but raw material was clandestinely obtained through "backdoor"
arrangements, and the secrecy surrounding the work was such that, in the backwash
of shock following the Stimson ultimatum, to preclude showing the results of
the effort to anybody but the Chief Signal Officer—even G-2 was proscribed. In
those Depression years funds were extremely difficult to get, especially in
view of the nervous secrecy engendered by the Yardley* disclosures. Perhaps
the greatest triumph of the Army cryptanalytic group at this time of stringency
and uncertainty was the establishment under the Signal Intelligence Service of
a training school for officers, which grew from a student body of one in 1931
to about a dozen ten years later.
* The American Black Chamber
by H. 0.
Yardley, Indianapolis: Bobbs Merrill, 1931.
8
When the newly established
Navy COMINT Unit began its study of Japanese diplomatic systems in 1924-25, the Army steadfastly refused to give the Navy any
assistance or to even admit that Yardley's "Black Chamber" in New
York City ever existed. In 1931 the Navy set an example of
collaboration by giving the Signal Corps all Japanese diplomatic keys which had
been recovered since the abolition of the Black Chamber plus full data on new
systems which had come into being since that date. The Army thereafter more or
less took over Japanese diplomatic systems, leaving the Navy free to devote its
efforts to Japanese Naval systems.
From that time on there was
complete interchange between the Army and Navy regarding all technical features
of Japanese diplomatic traffic, as well as the exchange of important
translations. During the winter of 1935-36,
a new Japanese
diplomatic system came into effect which the Army correctly estimated to be a
machine system. The Navy suspected that it might be similar to the Naval
Attaché cipher machine, which the U.S. Navy was currently reading, if not the
same machine. The Navy gave the Army full technical details of this machine,
plus "reconstructed" equipment, and techniques of its solution.
Shortly thereafter, the Army was reading the messages in this new diplomatic
system, subsequently called the "Red" machine. Later the Red machine disappeared
from major Japanese embassies and reappeared in less important diplomatic
posts. A new machine (subsequently called "Purple") with similarities
to the Red machine but more complex, replaced the Red machines in major
embassies.
As far as technical
difficulties were concerned, the Army's solution of the Purple machine was a
masterpiece of cryptanalysis in the pre-war era. Its solution required about
two years plus numerous "cribs" and expected texts, literally driving
some of the solution participants to the verge of nervous breakdowns. The Navy
assisted by fabricating compatible Purple machines at the Naval Gun Factory.
These were distributed to the War Department, Navy Department, CINCAF, and
subsequently to the British COMINT organization in London. Solution of the
basic Purple machine itself was not the whole story by any means, because a new
key was used each day and had to be recovered daily. Special keys for special
services were introduced later on, and these likewise had to be recovered. The
Navy assisted the Army in the recovery of the Purple daily keys and eventually
developed a system of "predicted keys," whereby older keys could be
re-used after going through certain manipulations. All important messages sent
from Tokyo to Washington on 6 and 7 December 1941 were in "predicted"
keys so the only delay in reading these messages was decoding and translating.
9
The Navy COMINT Organization
always recognized that its proper targets were the major Navies of the
world—particularly the Japanese Navy. It began solution of diplomatic systems
in 1924 for the training of personnel, because such traffic was on hand,
relayed by U.S. Naval Radio Stations. No Japanese Naval messages were then
available and there were no intercept stations or operators capable of copying
them. Work on Japanese diplomatic systems therefore was continued, partly for
training and partly to be independent of U.S. Army sources, to say nothing of
orders of higher authority. During the hiatus between the closing of Yardley's Black
Chamber and the establishment of the "revived" Signal Corps Unit in
Washington, the Navy was the only source of Japanese diplomatic COMINT and
attempts were made to translate as much diplomatic intercept as possible during
this period. For the rest of the time, up to 1938‑39, the Navy's interest
in Japanese diplomatic traffic centered on solving their ciphers and recovering
keys. The CinC Asiatic Fleet was kept supplied with Japanese diplomatic ciphers
and keys from 1931 through 1941, and his Fleet Intelligence Officer made
translations from the Japanese texts as were required by the CINCAF.
Even until 1938-39 the same
safe which previously yielded the Japanese Naval Code in the early 1920's
remained a never-failing source of supply for both "effective" and
"reserve" diplomatic ciphers and keys—with the exception of the two
Red and Purple machine systems. This enabled the Navy Department to provide
CINCAF, as well as the Army, with Japanese diplomatic ciphers and keys before
they actually came into use. At that time the U.S. Navy was devoting virtually
all of its cryptanalytic effort and about 90% of its translating effort to
Japanese Naval Codes and Ciphers, leaving Japanese diplomatic systems to the
U.S. Army. Later, during the winter of 1940-41, when the White House and the
State Department became seriously interested in Japanese diplomatic messages,
the picture changed.
Once the Purple diplomatic
system became readable, and the need for current solutions was felt, the War
Department's COMINT Unit* did not have enough Japanese translators to handle
the job efficiently. Furthermore, it was under heavy pressure to divert a
number of its cryptanalysts and crypto-clerks to the solution of German
cryptographic systems. Therefore, the Army requested the Navy to assist with
the reading of Japanese diplomatic traffic on a 50-50 division of effort.
10
After studying and rejecting
two earlier proposals, it was agreed to divide all Japanese diplomatic traffic
processing (decrypting or decoding) plus translation on a daily basis, the Navy
taking the odd days and the Army the even days. This was the simplest way to
evenly divide the workload and prevent duplication of effort. A few months
later Naval Intelligence and the Army's G-2 arranged for the dissemination of
Japanese diplomatic traffic to the White House and to the State Department on a
monthly basis, the Navy taking the odd months and the Army the even months.
The collaboration between
the Army and the Navy with respect to Japanese diplomatic crypto-systems did
not extend to Japanese Military (Army and Navy) systems. A secret divulged to a
third party is no longer a secret. The Navy, therefore, withheld all details of
its success with Japanese Naval systems from the Army; and in turn no inquiries
were made by the Navy to the Army regarding their progress with reading
Japanese Army systems. The Army likewise made no inquiries of the Navy.
When the Japanese Army
invaded Manchuria in 1931, the U.S. Navy intercept station at Peking (manned by
Marine Corps operators) went to a special watch condition and obtained a wealth
of tactical intercepts. These were turned over to the War Department for
exploitation—and no embarrassing questions were ever asked. Later, beginning in
1936, Navy intercept stations in the Far East copied considerable Japanese Army
messages which were likewise turned over to the War Department. However, for
some unknown reason the U.S. Army posts at Tientsin and Manila failed to profit
from this wealth of Japanese Army messages. Not until the spring of 1941 did
the War Department attempt to set up an intercept unit in the Philippines and
to this end sent a Signal Corps officer to take charge. The Navy collaborated
by making a three-month loan of an experienced and qualified Chief Radioman to
act as instructor, and further supplied available technical literature on
intercept operator training, Japanese radio procedure including their radio
organization, Japanese call-signs and address systems, etc. The Army was left
"on their own," however, insofar as the solution of Japanese military
systems were concerned.
On 1 December 1930 the old
1918 Japanese Naval Code was replaced by a 1930 Naval Code. When this latter
code was replaced eight years later, on 31 October 1938, the U.S. Navy COMINT
organization suffered a severe, though only temporary, setback. Since the new
code was an enciphered code, the cipher first had to be stripped off before the
basic code could be reconstructed. To make a long story short, the Navy
cryptanalysts, spearheaded by Mrs. Driscoll, "accomplished the
impossible." They solved the encipher-
11
ment and then reconstructed the code. This was the
most difficult cryptanalytic task ever performed up to that date and possibly
the most brilliant as there were no "cribs" nor "expected
texts" to help out as in the case of the Army's solution of the Purple
machine. IBM tabulating machinery was introduced by the Navy incident to the
solution of the 1930 Naval Operations Code. This equipment greatly speeded up
the solution effort and increased the overall output of the Decrypting Unit. In
1941 similar IBM equipment was sent to Pearl Harbor and to Corregidor.
The Japanese Navy held their
Grand Maneuvers every three years. With the Japanese Navy's 1930 Grand
Maneuvers fully digested in terms of communications intelligence, comprehensive
plans were made for the 1933 Grand Maneuvers. Later events proved that these
maneuvers were a dress rehearsal for the Conquest of China—while warding off at
the same time intervention from the U.S. Fleet. The U.S. Navy tested its
knowledge and theories of Traffic Analysis under simulated war conditions and
found them practicable and reliable. The success of the Asiatic CI Unit
convinced CINCAF (Admiral Upham) of the necessity of a permanent Navy COMINT
installation on Corregidor. The project was begun in 1938 and completed in
September 1941. On 7 December 1941 the Asiatic CI Unit consisted of nine
officers and 61 men. Located in a bomb-proof tunnel on Corregidor, they
functioned with complete efficiency. This Unit was subsequently evacuated to
Australia by submarine and played an important part in the Battle of Coral Sea
and in the Battle of Midway.
Extensive arrangements,
including a mobile intercept unit aboard a destroyer, were made to cover the
1936 Grand Maneuvers of the Japanese Navy. But these maneuvers were delayed and
finally turned into the real thing—the Invasion of China—as forecast by the
1933 Grand Maneuvers. The Navy COMINT organization gave the CNO and CINCAF
advance information on all important moves and this information was later
verified without exception. It proved what could be done by COMINT, even
without radio direction finders and high-frequency D/Fs, which we hoped were
"just around the corner." The 1930 Naval Operations Code was
thoroughly reconstructed by this time and the only limit to detailed knowledge
of what was going on inside the Japanese Navy was the acute shortage of
translators plus the fact that sometimes the Japanese did not entrust important
secret matters to radio communications. The "China Incident"
highlighted the need for a secure COMINT post in the Philippines. The
Corregidor Project was thus revived. This was after the CNO finally beat down
the objections of the Army Chief of Staff which delayed the project for two
years. The two years additional delay were due principally to obstinance on the
part of certain high
12
ranking
officers* in the Navy Department.
The most important and
certainly the most dramatic incident derived from the solution of the Japanese
1930 Naval Code was a message reporting the Nagato's post-modernization
trials in 1936. We were fortunate enough to intercept the message and obtain a
solid translation. The Nagato's speed was better than 26 knots—the same
as that of the four Kongo-class battle cruisers. There was no doubt as
to the correctness of this information. By inference, this was the prospective
speed of the modernized Mutsu and minimum speed for the new Japanese
battleships of the Yamato-class. This information created consternation
in the highest echelons of the Navy Department, because the Mutsu-class
had been believed good for only 23-1/2 knots, and our new battleships (then in
blueprint stage) were going to have a speed of only 24 knots. The information
was referred to the General Board and as a result the maximum speed for
battleships North Carolina and Washington was raised to 27
knots; for later battleships the maximum speed was raised to 28 knots. The
twelve battleships of our new building program were thus given a superiority in
speed over the Japanese battleships.** Unfortunately, it proved impossible to
get COMINT information on the tonnage, speed, or main-battery caliber of the
Yamato-class of ships. The Japanese never sent this information by radio.
On 1 June 1939 the Japanese
Navy introduced a new type of cryptographic system, a different enciphered code
system.
Mrs. Driscoll and Mr.
Currier spearheaded the attack against this new code and we were soon able to
reconstruct the basic code. Recovery of the encipherment keys, recovery of
additive, however, involved a great deal more labor and more personnel than
that required for the recovery of the earlier transposition keys. Main work of
solution was undertaken at Washington. By December 1940 we were working on two
systems of additives, both used with the same basic code book. The
"old" additives assisted in basic code recovery
* When Admiral Moreal was being briefed on the Corregidor Project a few days after taking office, he exclaimed, "Hell ‑ I don't need Congressional authorization to dig a hole in the ground! But I do need authorization before I put up any buildings. If the Chief of Naval Operations can get me funds for the Tunnel, I will start it immediately; and I will also get the funds for the buildings and take care of the Congressional approval."
* It is fashionable today to perhaps sneer at battleships, but when World War II was on and the Japanese battleships and heavy cruisers were active, our Naval aviators were glad indeed to see fast battleships in our Carrier Task Forces. A carrier, at night, is an easy victim to any heavy surface craft.
13
and the "new" additives were valuable for obtaining current information, i.e. reading current traffic.
In order to permit Japanese
traffic to be read as quickly as possible at the scene of potential action, a
set of "code-values," cipher keys, skeleton codebook, cryptanalytical
techniques, etc., earlier intended for Pearl Harbor, were diverted to
Corregidor. A replacement, however, was hastily prepared in Washington and sent
to Pearl Harbor, arriving in November 1941. On 10 December 1941, after the
Japanese attack at Pearl Harbor, the COMINT Unit there discontinued its
cryptanalytic attack on the Japanese Flag Officers' Cipher and concentrated all
effort on the enciphered code system introduced by the Japanese in 1939. The
Flag Officers' Cipher was never solved and the Japanese discontinued its use,
probably because of its slowness, complexity, and susceptibility to error. It was
the only Japanese Naval Cryptographic system which the U.S. Navy failed to
solve.
On 1 December 1941 the
Japanese enciphered code of 1939 suddenly became unreadable. CINCAF promptly
advised Washington to this effect. This could have been a tip-off as to coming
hostilities, but it also could have been merely a routine change of system.
After all, the code had been in use for 2-1/2 years. Two weeks later,
Corregidor flashed the good news that the same basic code was still being used,
but that a new set of additives was being used with it.* This was the third or
fourth set of additives used with this same code-book. By February 1942 the new
additives had been solved to a readable extent. This same basic code was
retained in use through the Battle of Coral Sea and the "build-up"
for the Battle of Midway. It was finally superseded on 31 May/1 June 1941 by
another similar basic code. If (and it is a big if), if the Japanese Navy had
changed the code-book along with the cipher additives on 1 December 1941, there
is no telling how badly the War in the Pacific would have gone for Australia
and the U.S. or how well for the Japanese in the middle stages. Without
detracting in any way from the cryptanalysts who spotted the actual tip-offs,
or from the men who did the fighting, great plaudits for Coral Sea and Midway
successes should be given to the Navy's pre-Pearl Harbor COMINT effort.
* "COM 16 TO OPNAV INFO CINCAF ‑ TOP SECRET ‑ 151250 ‑ TWO INTERCEPTS IN ... PLAIN CODE SIXTH AND THIRTEENTH FOLLOWED WITHIN A FEW HOURS BY ENCIPHERED VERSIONS CONFIRMED INDICATOR ... ALREADY RECOVERED BY MATHEMATICAL ELIMINATION PM CODE REMAINS UNCHANGED X WILL SEND ... RECOVERIES THIS SYSTEM IF YOU DESIRE BEGIN WORK ON CURRENT PERIOD."
14
The decryption of Japanese
Diplomatic messages in Washington throughout 1941 is now a matter of public
knowledge and some 40 volumes comprise the official record. We may summarize by
stating that the COMINT organizations of the Army and the Navy worked in
perfect coordination during this period and provided the White House, State
Department, Army General Staff and Naval Operations with authentic, timely and
complete information concerning the Diplomatic Crisis and the mobilization and
movements of Japanese amphibious forces for the conquest of Southeast Asia. The
White House and State Department used this information with consummate skill.
The failure of the General Staff and Naval Operations to profit from the same
information is beyond the scope of the present text. In this connection, the
Joint Committee on the Investigation of the Pearl Harbor Attack stated
"[We have] been intrigued throughout the Pearl Harbor proceedings by one
enigmatic and paramount question: Why, with some of the finest intelligence
available in our history, with the almost certain knowledge that war was at
hand, with plans that contemplated the precise type of attack that was executed
by Japan on the morning of December 7—why was it possible for a Pearl Harbor to
occur?" See Senate Document No. 244—79th Congress, page 253 (Recommendations).
As long as the Navy did all
its own interception and the Army relied on "back-door methods" for
its source of traffic there was no problem about "collaboration" or
"division of effort" in interception. But troubles arose when the
European War broke out and the Army's Signal Intelligence Service (SIS)* began
to establish intercept units at Army posts. The officers responsible for the
Army Intercept Service were strong on theory but weak on performance and
unwilling to profit by the greater experience of the Navy. Coordination and
consultations were considered by them to be more important than getting on with
the job. Weeks were wasted in fruitless conferences while the Army learned
"the hard way" while setting up their own interception system.
In 1940-41 the Army had no
intercept stations which could match the Navy's, which included Corregidor,
Bainbridge Island, Washington, and Cheltenham, Maryland. Navy intercept
stations contained directional antennas beamed on “target" transmitters, diversity
receivers to overcome fading, recorders for copying high speed automatic
transmissions, highly trained operators, and experienced supervisors.
Allocation of the intercept effort between the Army and Navy was finally
settled on a trial-and-error basis.
* The Army's Signal Intelligence
Service (SIS) later became known as the Army Security Agency (ASA).
15
The Army covered as many of the international commercial transmitting stations as it could, while the Navy covered the others as a matter of necessity. Theoretically it was bad to "split" the intercept coverage of a circuit, but practically there was no alternative. Assignments were changed almost weekly as radio propagation suffered seasonal changes, as more operators and more receiving equipment became available, and as the pressure from higher authority required speeding up the delivery and "bridging the gaps" in intercepted traffic regardless of cost.
Covering international radio
circuits is like fishing with a dragnet. Anything and everything comes in with
the haul. Then it is necessary to sort out the catch and discard what is not
wanted. Monitoring for Japanese diplomatic traffic automatically produced naval
attaché messages, military attaché messages, German diplomatic traffic, etc.
It is needless to review all
the arguments and discussions that took place in 1940. Not only did intercept
assignments between the services change from time to time during 1940 and 1941,
but the assignments to intercept stations within each service changed from time
to time. For example, we eventually found we could get the best coverage of the
Berlin-Tokyo circuit at Corregidor. Messages in the Purple system were
therefore re-enciphered in a Navy system and forwarded to Washington by radio.
During the last few weeks before the Pearl Harbor attack, while U.S.-Japanese
relations were at a crisis, Japanese diplomatic messages intercepted at
intercept stations in the continental U.S. (Bainbridge Island and Cheltenham,
for example) were relayed to Washington by landline teletype. Army intercepts,
on the other hand, continued to be forwarded to Washington, D.C. by mail even
after 7 December 1941. The Navy also arranged for "back-door"
services on all diplomatic traffic in and out of Washington and New York—to
back up the radio intercept stations.
The squabbles between the
Army and the Navy COMINT organizations were confined to the interception,
"processing," translation and dissemination of Japanese diplomatic
messages. These controversies settled themselves in the course of time, and in
retrospect are seen to have been merely petty annoyances.
In Japanese diplomatic
traffic the Navy found it had a bear by the tail and couldn't let go until
after the attack on Pearl Harbor. The Japanese diplomatic messages became
greatly reduced in volume and importance. By this time the Army was able to
handle all Japanese diplomatic decryption and translation, leaving the Navy
free to begin an attack on German submarine communications.
16
During November and early
December of 1941, Japanese diplomatic traffic was diverting 30 percent of the
Navy's Intercept and direction-finding effort, 12 percent of its Decrypting
effort and 50 percent of its Japanese translation effort from other military
functions. Loss of the translators hurt the Navy the worst, as the total number
of translators available was inadequate even to handle Japanese Naval messages.
Loss of analytic personnel was more serious than the numbers indicate because
our "first team" in Washington had to be assigned to the solution of
Japanese diplomatic traffic. Detailed breakdowns are given in tabular form
below.
Distribution
of Navy COMINT Personnel ‑ Early Dec. 1941 |
|||||
Category |
Atlantic (Navy Dept.) |
Pacific (Pearl Harbor) |
Asiatic (Corregidor) |
In Transit (Diverted to Australia) |
Total |
Officers |
53 |
12 |
9 |
6 |
80 |
Crypto‑Clerks |
157 |
18 |
19 |
20 |
214 |
Sub‑total |
210 |
30 |
28 |
26 |
294 |
|
|
|
|
|
|
Intercept
Stations & D/F Control |
178 |
72 |
42 |
— |
292 |
|
|
|
|
|
|
Outlying D/F Stations |
|
|
|
|
|
|
60 |
84 |
8 |
— |
152 |
TOTAL |
448 |
186 |
78 |
26 |
738 |
Allocation
of NEW COMINT Effort ‑ Early Dec. 1941 |
|||
|
|
|
|
Category
|
Japanese Diplomatic |
Japanese Navy |
German & Italian Navys |
Intercept,
D/F, & D/F Control |
30% |
50% |
20% |
|
(Includes all diplomatic interception) |
|
|
Decryption |
12% |
85% |
3% |
Translation |
50% |
50% |
None |
17
There were no problems of
collaboration between the Army and Navy for strictly military COMINT matters,
as each service was working alone in its proper sphere of activity. The Navy
COMINT team did a thorough job with respect to the Japanese Navy with no help from
the Army. No assistance was requested from the Army other than permission to
establish a Navy COMINT Unit on Corregidor. The Navy gave the Army all its
Japanese Army intercepts, assisted in training an Intercept Unit at Manila,
never denied the Army any legitimate information requested, and gave the Army
all the help it was willing to accept. The Army, in turn, provided the Navy
copies of all its technical cryptanalytical manuals and training courses.
A summary of the Navy's
pre-Pearl Harbor COMINT effort and COMINT concepts may be seen in the secret
letter (Serial 081420) sent by the Chief of Naval Operations to the
Commanders-in-Chief of the Asiatic and Pacific Fleets and to the Commandants of
the Fourteenth and Sixteenth Naval Districts, in October 1940, extracts from
which follow:
Subject: Cryptanalytical
Activities, status of.
1. In view of the present serious international situation, it is
desired to acquaint the addressees with the present status and prospects of
solution of Orange naval cryptographic systems . ...
2. During the past ten years, Orange intelligence has been provided
by solution of Orange cryptographic systems, and to a lesser extent by
direction finding and traffic analysis. Every major movement of the Orange
Fleet has been predicted, and a continuous flow of information concerning
Orange diplomatic activities has been made available . ...
3. There are five major Orange naval cryptographic systems in current
use, all of the enciphered code type, namely:
A. Administrative Code system.
The cipher used with this code changes every ten days. Code and cipher recovery
is in the hands of Commandant, Fourteenth Naval District, and has progressed to
the point where intelligible text can be obtained from nearly all intercepted
messages.
B. Merchant Ship Code
system.
The system itself is 99% readable, but an auxiliary system of ship and place
names has not yet been recovered. The cipher changes quarterly, and has been
predicted through June, 1941 . ...
18
C. Materiel Code system.
This code has its cipher changing at irregular intervals of from ten to thirty
days. Current information is not now being obtained from this system, but it is
estimated that within six months we will be able to read most of this traffic
shortly after receipt.
D. Operations Code system.
A cipher is employed with this code, and although the method of recovery is
well defined, the process is a laborious one, requiring from an hour to several
days for each message . ... Recovery is being pursued by the Department, and details
will be promulgated later.
E. Intelligence Code system.
This system, being of least importance, has been neglected in favor of the
others . ... Solution is being handled by the Department.
4. With regard to the immediate
dissemination of intelligence, it is incumbent upon the Communications
Intelligence Units to provide the proper authorities with information and
inferences obtained from Communications Intelligence. Since it is manifestly
impracticable for the Commander-in-Chief, U.S. Fleet, to gather such
information firsthand, and impossible for him even to use recovered
cryptographic systems without an Orange language officer on his staff, it is
desired that Commandant, Fourteenth Naval District, and Commandant, Sixteenth
Naval District, disseminate such intelligence from time to time to both
Commanders-in-Chief and to the Department. This will require that all messages
in readable Orange Navy systems be translated promptly upon receipt, to insure
intelligence of as fresh a nature as possible, and all cryptanalytical and
cryptographic activity must be subjected to this end. As a general rule,
readable Orange Navy encrypted communications should be handled in inverse
order of interception.
5. It must be borne in mind that the
present Orange cryptographic systems may be replaced by new ones immediately
upon the outbreak of war. Therefore, cryptanalytic intelligence, per se, may
not be available from that time until after successful attack has been
conducted. Meanwhile, enemy information can be obtained from radio intercept
and direction finder activities as has been the case during the past year.
(Signed)
R. E.
INGERSOLL
Acting