The Emperor's Codes: The Breaking of Japan's Secret Ciphers
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Breaking the Emperor's codes
The conventional notion about code-breaking in World War II was that the British cracked the German Enigma machine, and that the Americans cracked the Japanese Purple code, and that throughout the war both countries merrily read the transmissions of their enemy. This was of course very far from the case.
In the first place, messages were both coded and enciphered. For example, the Japanese navy had about 30,000 five-digit code groups to cover just about every term that might be used in a message. Once encoded, the message would be enciphered in any number of ways, for example, by arranging the coded message in a grid 10 figures wide and 10 figures deep, starting from left to right; then taking the figures off the grid vertically or even at a diagonal; then using an "additive" number to further baffle the codebreaker. If a codebook was captured, the code would be changed. And occasionally the enciphering system was also changed. So breaking enemy messages was a process that was never entirely complete (there was always some guesswork) and that never ended (because the enemy would change the rules from time to time.)
Take the famous "East Wind Rain" message, for example. Every western power knew in November 1941 that "east wind rain" when added to the regular weather broadcast would mean war upon the United States (there were other phrases to indicate war on British and Dutch possessions). In Foreign Relations of the United States for 1941, for example, there appears a translation of this message, forwarded by the Dutch to the U.S. But the actual broadcast was either never made, or it was not intercepted, or if intercepted was not decoded. Enemy broadcasts were never an open book, even toward the end of the war.
Michael Smith tells the story of the Japanese intercepts from the point of view of the British code-breakers, with due attention to the somewhat more impressive American efforts. Indeed, the differences between them--the British relying mainly on eccentric geniuses, the Americans on sheer manpower and material resources--is a fascinating glimpse of the contrasting strength of the two major Allied powers. (The complexity of British code-breaking organizations is also typical, and has been remarked upon by such "British" clandestine operators as Terence O'Brien, who admired the OSS for its straightforward organization if not for its choice of allies and enemies.)
The U.S., of course, also had its internal rivalry, but it was a very simple one: the U.S. Navy against everyone else. The Navy never cooperated with the British until the latter were producing intelligence of such value that the Navy wanted it, at which the Navy changed its ways. This too is confirmed by other sources. The U.S. Navy too often seemed to look upon the U.S. Army as its primary antagonist, with the British second and the Japanese bringing up the rear.
Code-breaking is mind-bending stuff, and Michael Smith didn't entirely clear it up for me. His book might be easier reading for someone already interested in codes and code-breaking. Splendid stuff, in any event.