Closing the book on Pearl Harbor

Cryptologia, Apr 2000 by Budiansky, Stephen

When it first appeared, the Operations Code was referred to as the "five numeral system (Orange Navy)," Orange being the standard U. S. Navy codename for Japan. By August 1940 it was designated AN, and by spring 1942 it was redesignated JN-25; the latter is the name by which it is now most commonly referred.

Stinnett attempts to make much of the fact that one decrypt he found in the National Archives files is of an Operations Code message which, according to intercept logs he has examined, was intercepted on November 18, 1941, but which bears the later designator "JN-25B." Above the caption "evidence of falsification" Stinnett presents a photocopy of the decrypt, and states, "The designator JN-25-B was applied to this code in late 1942 or 1943 by the Navy, but because of censorship at the time of writing of this book in 1998, the exact date cannot be determined. By pretending that this original dispatch was transmitted by Japan in JN-25-B, Navy censors have convinced many historians that this message text was not available until 1942 or later." 7 This is a mindboggling argument, as perfect an illustration of begging the question as one could ever hope to find. Because he has convinced himself that the Navy was reading the Operations Code in November 1941, Stinnett concludes that intercepting a message was tantamount to decrypting and reading it. Thus, if the decrypt of a message intercepted in November 1941 bears the designation JN-25-B, the only possible explanation is that this is a "falsification." In fact, the explanation is perfectly simple. This message, along with thousands of others transmitted by the Japanese during 1941, was indeed intercepted by the United States Navy's listening stations at the time of its transmission. It was copied, logged, passed on to the Navy codebreaking units at OP-20-G headquarters in Washington and at Hawaii, and that was that. It was riot broken and read, however, until 1946 when, the war safely won, OP-20-G decided to tidy up loose ends and go back to the accumulated raw intercepts from the pre-Pearl Harbor period. It is a standard signals-intelligence procedure to type the date of decryption (and sometimes separately the date of translation, if there was a delay) at the bottom of decrypts; thousands upon thousands of decrypts from World War II in the files of the National Archives follow this practice. At the bottom of this particular decrypt appears the words, "Navy Trans 4/24/46." Stinnett predictably concludes that this date is also "evidence of falsification," since he knows that it was actually broken before Pearl Harbor. As absurd as it sounds, that is the sum of his argument. He presents no conclusive evidence of any kind that any Operations Code messages from 1941 were actually decrypted before December 7; he merely assumes his conclusion and marches around a logical circle. The facts that texts of some of these pre-Pearl Harbor messages were published in a post-war history, or that these message were logged in (but not decrypted) by the intercept station at Hawaii, both facts that Stinnett deems highly significant, in fact mean absolutely nothing.8