I've had much more fun at surprising David Kahn with a transcribed copy of Yardley's suppressed book. Actually, it is a rather tedious account, (about 1500 pages in length), which probably would only be of interest to a few cryptological historians; but, it provided me with enough backstory to the American and Japanese intrigues at an international disarmament conference, (twenty years before the attack at Pearl Harbor), for a screenplay.
The Cipher Bureau is best known for its work during the Washington Conference of 1921-22 and the resultant Five-Power Naval Treaty. This gathering was an attempt to limit the size of postwar navies and thus head off an international arms race.
During the conference, Yardley himself, with assistance from his staff, solved the cipher used by the Japanese representatives to this conference.
The decrypt intelligence produced by the Cipher Bureau during the Washington Conference was of mixed importance. Some was timely and revealed the Japanese government's internal discussions (and dissents) over its negotiating position for the conference. Some of the Bureau's translations were late and covered information already revealed in the press -- but even these decrypts had value, since they confirmed or refuted media reports that were of unknown validity.
The Washington Treaty imposed a limit on capital ship tonnage by the major powers. Yardley's decrypts helped the U.S. negotiators encourage Japan to accept its minimum position rather than hold out for a higher tonnage level.
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