Today, 87 years ago:

Although the first class of On the Roof Gang (OTRG) convened on 1 October 1928, the history of OTRG started in 1921, when the Office of Naval Intelligence (ONI) covertly acquired a photographic copy of the “Imperial Japanese Navy Secret Operating Code-1918.”  The code was in essence a dictionary containing a hundred thousand entries, and it took five years to translate.  There were only two Japanese linguists available, and there was no urgency or incentive to complete the project.  After all, having a code book is of no great advantage if one does not have access to messages being encoded 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 did 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 Morse code.  Kata Kana, sometimes referred to as “hen tracks,” is a simple pictorial means of phoneticizing the Japanese spoken language.  In 1923, the Chief of Naval Operations (CNO), perhaps unaware of the nature of the Japanese telegraphic code, requested that Asiatic and Pacific fleet radio operators listen in their spare time for enciphered/ encoded foreign radio messages.  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.  Whether anyone in Washington was aware of his accomplishment at the time is not clear, but it paid enormous dividends in years to follow is an indisputable matter of record.

 
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, LT Laurence F. Safford at OP-2-G in Washington, one of the first U.S. naval officers to specialize in the new field of cryptology, purchased a few specially designed Japanese typewriters.  In that same year, the first shore-based intercept station was established in the American consulate in Shanghai (Station ABLE).  Its primary target was the diplomatic radio network serving the numerous Japanese consulates throughout China.  In 1935, Station ABLE was disestablished when the Japanese threat to the city became too pressing and personnel limitations caused the Marine Corps to withdraw.  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.
 
In 1926, ONI finally finished translating the 1918 Japanese Navy code book, acquired in 1921.  Code book updates were obtained, again covertly, 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.  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 to 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.  The graduates of this school were eventually recognized 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 on 1 October 1928.
The first class was considered a success, so five more were held in 1929. The instructor for the first three was Chief Radio Harry Kidder.  The last two were taught by Chief Radioman Dorman Chauncey.  Both were veterans of intercept operations in the Asiatic Fleet.  Chief Chauncey had conducted intercept at the U.S. Navy sites in Hawaii and Peking.  There were a total of 176 graduates that completed the course (150 Sailors and 26 Marines) from 1928 to 1941.
NOTE (1): The Navy Building in the District of Columbia was demolished after World War II. Part of the area where it once stood is now where the Vietnam Memorial is located.
NOTE (2): Building 511 on Corry Station in Pensacola, Florida is named after Chief Radioman Harry Kidder.  This building is where the majority of Morse code training was accomplished during the 1970s and 1980s using the RALPH Morse code trainer.
 
Sources:
  • Laurance F. Safford, “A Brief History of Communications Intelligence in the United States”
  • Jack S. Holtwick, Jr. (Capt., USN), comp., “Naval Security Group History to World War II”
  • P. L. Phillips, “Kidder First OTRG Instructor,” Cryptolog, Summer 1983
  • Edwin T. Layton with Roger Pineau and John Costello, And I Was There (New York: Morrow, 1985)