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Historical Events
Historical Events | Aug. 20, 2021

Early Japanese Systems

[NOTE: In the following discussion, please be careful not to confuse RED and RED BOOK]

Like many countries around the world, the Japanese used a variety of cryptographic systems, often based on code books. As with many other countries, the Japanese shifted some but not all of their communications security to machine systems in the 1920s and 1930s, as the reliability of cipher equipment improved. The Japanese Navy continued to use a code book system, and, of course, the U.S. Navy was interested in finding out as much as it could about it.

On at least one occasion in the late 1920s, the U.S. Navy undertook what was euphemistically called "practical cryptanalysis," i.e., the Japanese embassy was entered surreptitiously and code books were photographed. The first instance resulted in what the Navy called the RED BOOK, a loose-leaf scrapbook bound in imitation leather, containing photos of a Japanese navy code. (Note: the designation "RED BOOK" was bestowed by the U.S. Navy, based on color of the binder in which the translation was kept).

The RED BOOK, which contained 100,000 entries, was translated by a missionary couple, and typed; only two copies were made. Four copies were typed of this translation in 1929, and distributed: one copy remained with OP-20-G, one was sent to the Asiatic Squadron, and two copies were placed in reserve.

When some RED BOOK messages were solved, primarily by Lieutenant Joseph Rochefort and Mrs. Agnes Driscoll, they revealed invaluable information about the Japanese Navy training and supply situations.

But the RED BOOK had an importance to U.S. Navy COMINT activities quite apart from the information developed from it. In the short term, it gave the CA people a reliable list of vocabulary likely to be included in future code book versions. From a wider perspective, it is clear that the success in decrypting Japanese messages helped convince senior Navy officials to build up the COMINT service.

The RED BOOK was followed in December 1930 by the BLUE BOOK, a system of about 85,000 code groups. Since no copy of that was available, U.S. cryptanalyts had to solve it the hard way. Then LT j.g Thomas Dyer was given the task, and, after a key suggestion by Agnes Driscoll, was successful.

Subsequent solution of BLUE BOOK messages produced exceedingly useful information. Messages showed that Japan's new battleships had a speed in excess of 26 knots -- 2 knots faster than new battleships under construction in the United States (which had been based on incorrect assumptions that the Japanese ships would do only 23.5 knots). The U.S. Navy thus began planning for new battleships of 27 knots.

The Japanese replaced the "BLUE BOOK" in October 1938. Its successor was dubbed JN-25 by the American cryptanalysts, and will be dealt with in a later article.

In the early 1930s, possibly sparked by Yardley's published revelations about success in solving systems, the Japanese began to deploy more sophisticated cryptosecurity. About that time, the Japanese Navy sought to purchase a machine system from Boris Hagelin, a Swedish businessman then in the process of building his commercial cipher machine company. Hagelin was apprehensive that the Japanese would purchase sample machines, then use them as the basis for new machines without regard to his patent rights. He therefore only sold them some obsolete equipment invented much earlier by his late partner Arthur Damm.

Hagelin's fears were well founded. In fact, the Japanese government took the Damm machines, "reverse engineered" them, and created their own family of cipher devices. The derivative machines were used by the Japanese fleet, by Navy attaches, and by the Japanese Foreign Office.

The Japanese called their version the 91 Siki angooinziki, i.e., '31 model cipher machine. (1931 by the western calendar was year 2591 in the Japanese).

It eventually led to the diplomatic machine known to the American Army as RED, as well as to a Naval attache machine known to U.S. Navy cryptanalysts as, well, Naval Attache RED or "M-1." The M-1 was solved by Agnes Meyer Driscoll, Technical Assistant to the Officer in Charge, in 1934 or 1935. An American version of the machine was built at the Washington Navy Yard to expedite solutions.

The original naval version required the user to crank a handle after every letter; the Japanese Navy redesigned the machine, making it a completely electrical and thus a more efficient version, a machine they called the 97 Siki Inziki (or, '37 model printer). The diplomatic variant of this machine was known to the Americans as PURPLE, while the Naval attache and fleet versions were known as CORAL and JADE, respectively.

Apparently, the JADE machine did not stand up to heavy usage in the field, and, after an initial high volume of traffic, it was used much less.

One of the users of CORAL was Vice Admiral Abe (pronounced "Ah-bay," but nicknamed by Americans "Honest Abe"). As representative to an Axis military council, he passed considerable information about German deployments in CORAL; even though it was a Japanese system, it was essential for Allied military decision making in the European Theater.



  • Philip H. Jacobsen, "The Japanese Cipher Machines," NCVA (Paducah, Ky.: Turner Publishing Company, 1996), pp. 54-55.
  • Albert Pelletier, "Cryptography -- Target Japan," NCVA (Paducah, Ky.: Turner Publishing Company, 1996), pp. 27-32.
  • Francis A. Raven, "Some Notes on Early Japanese Naval/Diplomatic Cipher Machines," CCH Series File, IV.W.III.23.
  • L. F. Safford, Memorandum for Lieutenant Commander Raven, "Subj: History of Japanese Cipher Machines," 3 February 1944.
  • L. F. Safford, The Undeclared War: History of R.I., 15 November 1943.