ADM Upham also originated the “Corregidor Project”, won over the local Army authorities, and (after his transfer to the General Board) finally obtained the consent of the Chief of Staff, U.S. Army. From this time on, the Commander-in-Chief, Asiatic Fleet, looked upon the R.I. Unit as the most important facility under his command.

It may be added that on 7 December 1941 the Asiatic R.I. Unit consisted of nine officers and 61 men, located in a bombproof tunnel on Corregidor, and that it was functioning with an efficiency of 100%.

The Navy Department had been given almost complete information and warning of the Japanese intentions through the Navy’s Radio Intelligence Organization (R.I.O.), which was directly under my command from 6 May 1936 until 14 February 1942. From 1 September 1941 through 7 December 1941 we were in a solid position. The Navy’s high frequency direction finder stations at Corregidor, Guam, Pearl Harbor, Dutch Harbor, Samoa, and Midway were keeping us informed as to the general locations and compositions of Japanese naval forces. An idea of their efficiency may be gathered from the tracking charts submitted the previous year. (Enclosures to COM 14’s Secret

Serial 432 dated 24 September 19401. The direction finders also tracked the withdrawal of Japanese merchant vessels to Japanese home waters, beginning the first of October and ending in the middle of November 1941, when there were no longer any Japanese merchant vessels at sea. The Navy had solved the primary Japanese Fleet system to a partially readable extent, after being “out” for several months, and also was reading the “minor” Navy systems. Only the Japanese “Admirals” Cipher” still defied solution.  The Army had acquired a model of the Japanese Diplomatic Cipher Machine and the original set of cipher keys used with it (A).  LCDR D.W. Seiler, USNR, built the Navy three “Chinese copies” at the Washington Navy Yard, and the Amy built three or four models for itself.  Two of these machines (one Army and one Navy) plus key lists were turned over to the British Government. The Navy had solved or stolen all of the other Japanese Diplomatic Systems and had turned copies over to the Army and the British Government. The two services were working together on Diplomatic messages, the Navy being responsible for all messages originating on odd days and the Army for even days. We had worked out a system of “predicted keys” for the Machine, which were good for about half the future dates. We generally solved new keys within twelve hours. Messages in the machine system were forwarded by teletype or enciphered and forwarded by radio. New keys in the secondary system usually were solved within 24 hours, but the messages were forwarded by mail and were from five to ten days old when received (peacetime economy). Changes in the minor diplomatic systems were usually worked out in about seven days.

In early December 1941, the Navy’s “Asiatic R.I. unit” consisted of a total of 70 men (9 officers, 19 crypto clerks, and 42 intercept operators), located in a bombproof tunnel on Corregidor. It worked primarily against the Japanese Navy but it also covered diplomatic messages passed between China, Manchuria, the N.E.I., and Japan, using “keys” furnished by the Navy Department. The Navy’s “Hawaiian R.I. Unit,” consisting of a total of 100 men (15 officers, 24 crypto clerks, and 60 intercept operators), tracked Japanese ships and worked on Japanese naval messages exclusively. Liaison and exchange of technical information and translation was maintained between Corregidor and Singapore by the U.S. Navy: between Washington and London by the U.S. Army for decryption and by the U.S. Navy for D/F bearings.

The Diplomatic Section of the Navy Department Decrypting Unit had been standing 24-hour watches, seven days per week, since February first, 1941. It had an organization of four sections, with one officer and three experienced petty officers per section, plus four “idlers” and three translators – a total of 23 persons. The Army had approximately the same number working on Japanese diplomatic messages. Our Japanese translators worked on a two-section basis: normal office hours plus one translator who came down at night and stayed until about midnight or until everything had been cleaned up. An Adventist Missionary (who “observed his Sabbath on the Sabbath Day”) normally took the Sunday duties. This was a very efficient arrangement as it took some time to verify the new day’s key or to solve it, and more time to decrypt intercepted messages. As a general rule, a translator was not needed until about the time he came on duty at 8 o’clock in the morning, and priority messages intercepted during the night or early morning were decrypted and translated by 10 a.m. The War Department Decrypting Unit observed normal office hours up until the evening of 6 December 1941; but some of their people came down when warned by us, and they maintained continuous watch from that time on. The Navy not only deciphered and translated all messages for its “day of responsibility,” over weekends and after office hours. There was a daily exchange of translations between the Army and Navy as well as special exchange when anything of particular importance came up.


Every Japanese diplomatic message that could be intercepted by the U.S. Army and Navy was promptly decrypted and typed smooth, ready for translation. Our shortage of translators in both services prevented translations of all messages, but we were able to translate the more important ones. All messages in the Machine were translated without fail. Messages were decrypted as soon as the new key was solved, although there was occasionally a lag in translation. Most messages classified as urgent (by the Japanese Government) and most “circular” messages in the minor systems were glanced over and if the beginning of the message did not indicate anything of importance the message was set aside to be translated at a slack period, and in many cases was never translated at all. The shortage of translators also made it undesirable for the Hawaiian Decrypting Unit to handle diplomatic messages, and this unit, therefore, was not furnished the “keys” for Japanese foreign-office systems. The small decrypting units of the War and Navy Departments were handling practically all the radio messages sent or received by the Japanese Foreign Office, and in most cases solving the cipher to boot. The “output” per man was stupendous and the time lags negligible for the important messages. It was not humanly possible, with the personnel available, to decrypt and decipher everything and a rigid system of priorities had to be observed in order to get the “hot” messages translated and disseminated without due delay. Despite the lack of experience of many of our naval reserve officers and enlisted men, the Navy’s “Radio Intelligence Organization” was operating at 99% efficiency in November and December, 1941.

LCDR A.D. Kramer, USN, in command of my Translating Section, segregated and cross referenced all messages, and briefed the more important ones. Daily at 11:00 a.m., Kramer would show the file to the Director of Naval Communications  (RADM Leigh Noyes), to the Director of Naval Intelligence (RADM T.S. Wilkinson), the Officer-in-Charge of the Far Eastern Section (ONI) CDR A.H. WcCollum), and the Assistant Chief of Naval Operations (RADM R.E. Ingersoll). Important messages were also shown to Director War Plans Division (RADM Turner). The more important messages, as designated by the Assistant C.N.O., were shown to the Chief of Naval Operations (ADM H.R. Stark) and the Secretary of the Navy (The Honorable Frank Knox). The message files were then turned over complete to the Naval Aide to the President (RADM J.R. Bearall) who took them to President Roosevelt and returned them to Kramer. The Secretary of State (The Honorable Cordell Hull) and the Under Secretary of State (The Honorable Sumner Welles) were also shown these messages, COL Bratton, U.S. Army, being responsible for delivery. On one occasion the President read the Japanese Ambassador’s secret report of a private audience with him. He was much impressed and commented, as he read the translation. “Yes, I said that”; “That is correct, he said that”; etc. I do not recall whether this was in Kramer’s presence or told to Kramer by ADM Beardall. After that, President Roosevelt never doubted our decryptions or translations.

(A) According to William Friedman, the Army acquired broke the through cryptanalytically.

By L. F. Safford, Captain, USN