Piercing the Fog - Air Force Historical Studies Office

Piercing the Fog
decision makers, one must assume a degree of influence. During the last twelve
months of the war in the Pacific, analyses in the MAGIC Summaries on the
economic impact of the AAF' s strategic bombing campaign increased, attesting
to the devastating impact that the American air attacks were having upon both
the civilian economy and domestic opinion.'85
Such influence by air intelligence specialists grew slowly until late 1943.
MAGIC analysts themselves recognized that much of the intelligence with air
implications derived from diplomatic sources was, in fact, secondhand.
Examples of such information that became available to the Allies were the
delicate Japanese-Russian negotiations over neutrality, the sporadic and
unsuccessful attempts by the Axis to break the Allied sea blockade with the use
of German and Japanese submarines, the shifting diplomatic and political
situations in Indochina and Thailand, the anti-British activities of the Indian and
Burmese puppet governments, and the Japanese attempts at peace negotiations
with Chungking. In mid-1943, the MAGIC summaries included several major
studies on Japanese military budget expenditures in Thailand and Indochina
which provided evidence of military initiative there as well as detailed analyses
on various aspects of the Japanese war economy, including rice, pig iron, and
aluminum production and rail transportation. But these had little immediate
tactical application in the Pacific air war.186
Another reason for the lack of high-level air intelligence in 1943 lay in the
periodic inability of American code breakers to decrypt Japanese Army or Navy
codes. * Unlike the Japanese MAGIC diplomatic messages, which were
enciphered by an Enigma-type machine and could be deciphered by the
American PURPLE device, the Japanese Army and Navy high-level codes were
enciphered by use of conventional but very difficult code books. The U.S. Navy
broke the Japanese JN-25 naval code first, in part because there were more navy
than army messages available for study. The Japanese Navy codes could be
deciphered by early 1942, although portions of many messages were often
unclear. For a time after January 1943, when a submarine loaded with code
books was captured, most naval codes could be deciphered. Japanese Army
codes began to yield in the spring of 1943, but they could not be broken
consistently until early 1944, when Allied forces captured a truckload of code
books. Even when coded messages could not be read, however, SIGINT gained
valuable information from traffic analysis by establishing locations of enemy
transmitters with radio direction finders and noting their signals activity.
Because the Japanese naval air forces were more security minded, American
SIGN was more successful against army air units, gradually establishing air
OBs, patterns of flight, types of aircraft, airfields in use, and eventually tracking
tail numbers of aircraft moving in and out of the forward area.18'
*The Japanese had no independent air force; the Japanese Army and the
Japanese Navy maintained their own air forces.
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