By Captain Duane L. Whitlock, U.S. Navy, Retired

ON THE DAY THE BOMBS FELL on Pearl Harbor, the U.S. Navy, or at least a tiny segment of it, had had the Imperial Japanese Navy under attack for about twenty years. The attack was, of course, a silent one, of which the Japanese were totally unaware. It began in 1921, when the Office of Naval Intelligence (ONI) surreptitiously acquired a photographic copy of the “Imperial Japanese Navy Secret Operating Code 1918.” [1] The code was in essence a dictionary containing a hundred thousand entries, and it took five years to translate; only two Japanese linguists were available, and there was no particular urgency or incentive attaching to the project. After all, having a code book is of no great advantage if one does not have access to messages being encrypted in that code.

ONI at the time did not have that access, and gaining it was not a simple matter, because the Japanese use a different telegraphic code for radio communications than does the rest of the world. Keyed to the Japanese alphabet, or syllabary, known as Kata Kana, it contains nearly twice as many dot-and-dash combinations as the Morse code. Kata Kana, sometimes referred to as “hen tracks,” is a simple pictorial means of phoneticizing the Japanese spoken language. In 1923, Admiral Edward W. Eberle, the Chief of Naval Operations (CNO) (1923-1927), perhaps unaware of the nature of the Japanese telegraphic code, requested that Rear Admiral Thomas Washington, Commander in Chief, Asiatic Fleet direct Pacific fleet radio operators listen in their spare time for enciphered foreign radio messages. [2] To what extent this invitation served its purpose is unknown, but several Navy and Marine Corps operators in the Far East did teach themselves to recognize and intercept Japanese radio communications. One of these operators, Chief Radioman Harry Kidder, was serving in the Philippines. With the help of the Japanese wife of a shipmate, he learned the Kata Kana syllabary, taught himself the telegraphic equivalents of all the Kata Kana characters, and began to intercept Japanese messages. [3] Whether anyone in Washington was aware of his accomplishment at the time is not clear; that it paid enormous dividends in years to follow is an indisputable matter of record.

Thomas Washington as Rear Admiral Commander in Chief, Asiatic Fleet,
October 11, 1923 to  October 14, 1925

A few other operators on the Asiatic Station somehow learned to write Kata Kana characters and copy Japanese messages with a pencil, though none ever gained the stature of Harry Kidder. Initially, intercept operations were uncoordinated and piecemeal, carried out on board only the one or two ships of the Asiatic Fleet that happened to boast a self-trained Kana operator. In 1924, to obtain more legible copy and eliminate writer’s cramp, Washington purchased a few specially designed Japanese typewriters (RIP-5). [4] In that same year, the first shore-based intercept station was established, in the American consulate in Shanghai. [5] Its primary target was the diplomatic radio network serving the numerous Japanese consulates throughout China. In 1927, this network became the prime target also of self-trained Marine Corps operators at the Marine detachment in Peiping (as it was then known, modern Beijing). Originally designated, in the phonetic alphabet of the time, Station ABLE, their unit was disestablished eight years later when both the Japanese threat to the city became too pressing and personnel limitations caused the Marine Corps to withdraw completely from intercept work. Responsibility for the diplomatic network was shifted to the headquarters of the Fourth Marine Regiment in Shanghai, which possessed an enclave of career Navy intercept operators trained in Japanese traffic. Their unit became the new Station ABLE. [6]

In 1926, ONI finally finished translating the 1918 Japanese Navy code book, acquired in 1921. Code book updates were obtained, again surreptitiously, in 1926 and in 1927. Given the cover-name “Red Book,” the translation was turned over to the Director of Naval Communications (DNC), for whom it served as a constant incentive to build up a radio intelligence organization. [7] Having the code but not the skilled personnel needed to intercept Imperial Japanese Navy (IJN) messages in significant quantity, the DNC, with the assistance of ONI, set about carefully screening and selecting a few well qualified fleet radio operators. To train them in Kata Kana and the Japanese telegraphic code, a school was set up in a specially constructed blockhouse on the roof of the old Navy Department building in Washington, D.C. (Graduates of this school were eventually venerated as the “On the Roof Gang.”) The search for a qualified instructor turned up Chief Kidder, who happened to be serving in the Navy Department communications center. The school opened in October 1928, and in the next eighteen months Kidder trained and graduated three classes. [8] Eight graduates were sent to Guam, where, under the tutelage of another self-taught Kana operator, Chief Radioman Malcolm Lyon, they established the Navy’s second intercept site, Station BAKER.

Scarcely had this site come into existence when, in 1930, the nine enlisted men stationed there scored an intelligence coup of historic significance. Monitoring Japanese naval communications, they were able to deduce from patterns alone that the entire fleet had sortied from Japan and was engaged in an exercise of massive proportions. The Japanese navy had even managed to call up all its reserve ships and personnel and send them to sea with the rest of the fleet, all with such secrecy that the U.S. naval attaché in Tokyo was unaware of anything unusual. [9] The material intercepted by Station BAKER slowly made its way to Washington. There the small cryptanalytic staff labored on it for many months, using the Red Book, ultimately decrypting enough to discover that the activity detected by Guam had been a triennial “Grand Maneuver,” in this case a test of a Japanese navy plan to support an invasion of Manchuria-as would take place the following year. [10]

This episode pointed up the dire inadequacy of the funds and facilities devoted to the intercept and processing of Japanese navy radio communications. To serve the two senior admirals in the Pacific theater, major decrypting units were needed in Hawaii and in the Far East, with many trained intercept operators, cryptanalysts, and Japanese linguists. Developing a radio intelligence organization of this scope fumed out to be a long-range project, and it was not completed before the outbreak of the Pacific war. In fact, were it not for the nudge given in 1930 by Station BAKER, there is substantial reason to believe it would not have been ready in time to contribute to the battles of Coral Sea and Midway. As it was, the Guam operators had alerted authorities to the possibility of deriving intelligence from enemy communications without actually decrypting the messages.


1. Laurance F. Safford, “A Brief History of Communications Intelligence in the United States,” Special Research History, National Archives, Modern Military Branch, Military Archives Division [hereafter SRH], no. 149, 21-7 March 1952, p. 6; and Laurance F. Safford, “History of Radio Intelligence: The Undeclared War,” SRH-305, 15 November 1943, pp. 03-05. Back

2. Jack S. Holtwick, Jr. (Capt., USN), comp., “Naval Security Group History to World War II,” SRH-355, June 1971, pp. 39-40. Back

3. P. L. Phillips, “Kidder First OTRG Instructor,” Cryptolog, Summer 1983, p. 9; and Edwin T. Layton with Roger Pineau and John Costello, And I Was There (New York: Morrow, 1985), p. 474. Back

4. Holtwick, SRH-355, pp. 40-1. Back

5. Ibid., pp. 37-40; and “A Brief History of the Radio Security Station Fourth Marine Regiment, Shanghai, China,” SRH-179, p. 2. Back

6. “A Brief History of the Radio Security Station Marine Detachment, Peiping, China,” SRH-178, pp. 6-8; and SRH-179, pp. 8-11. Back

7. Safford, SRH-305, pp. 03-05. Back

8. Phillips, p. 9. Back

9. Safford, SRH-305, p. 06. Back

10. Safford, SRH-149, p. 12; and Safford, SRH-305, p. 06 Back

Source: Naval War College Review, Vol. 48, No. 4 (AUTUMN 1995)

Featured Image: Admiral Edward W. Eberle, the Chief of Naval Operations (CNO) (1923-1927)