Pearl Harbor Advance-knowledge Conspiracy Theory - Assertions That Japanese Codes Had Already Been Broken

Assertions That Japanese Codes Had Already Been Broken

U.S. signals intelligence in 1941 was both impressively advanced and uneven. In the past, the U.S. MI-8 cryptographic operation in New York City had been shut down by Henry Stimson (Hoover's newly appointed Secretary of State), citing "ethical considerations", which inspired its now broke former director, Herbert Yardley, to write a 1931 book, The American Black Chamber, about its successes in breaking other nations' crypto traffic. Most countries responded promptly by changing (and generally improving) their ciphers and codes, forcing other nations to start over in reading their signals. The Japanese were no exception.

Nevertheless, U.S. cryptanalytic work continued after Stimson's action in two separate efforts: the Army's Signal Intelligence Service (SIS) and the Navy's Office of Naval Intelligence (ONI) crypto group, OP-20-G. Cryptanalytic work was kept secret to such an extent, however, commands such as the 14th Naval District at Pearl Harbor were prohibited from working on codebreaking by Admiral Kelly Turner as a consequence of the bureaucratic infighting in Washington.

By late 1941, those organizations had broken several Japanese ciphers, such as J19 and PA-K2, called Tsu and Oite respectively by the Japanese. The highest security diplomatic code, dubbed Purple by the U.S., had been broken, but American cryptanalysts had made little progress against the IJN's current Kaigun Ango Sho D (Naval Code D, called AN-1 by the U.S.; JN-25 after March 1942).

In addition, there was a perennial shortage of manpower, thanks to penury on one hand and the perception of intelligence as a low-value career path on the other. Translators were over-worked, cryptanalysts were in short supply, and staffs were generally stressed. Furthermore, there were difficulties retaining good intelligence officers and trained linguists; most did not remain on the job for the extended periods necessary to become truly professional. For career reasons, nearly all wanted to return to more standard assignments. However, concerning the manning levels, "... just prior to World War II, had some 700 people engaged in the effort and, in fact, obviously having some successes." Of these, 85% were tasked to decryption and 50% to translation efforts against IJN codes. The nature and degree of these successes has led to great confusion among non-specialists. Furthermore, OP-20-GY "analysts relied as much on summary reports as on the actual intercepted messages."

The U.S. was also given decrypted messages by Dutch (NEI) intelligence, who like the others in the British-Dutch-U.S. agreement to share the cryptographic load, shared information with allies. The U.S. refused to do likewise. This was, at least in part, due to fears of compromise; sharing even between Navy and Army was restricted. The eventual flow of intercepted and decrypted information was tightly and capriciously controlled. At times, even President Roosevelt did not receive all information from code-breaking activities. There were fears of compromise as a result of poor security after a memo dealing with Magic was tossed in the wastebasket of Brigadier General Edwin M. (Pa) Watson, the President's military aide.