US Army Codebreakers and the War against Japan

Abstract

Perhaps the most fruitful approach to reassessing the Pacific War is from the view­point of the accomplishments of US Army codebreakers. Since the mid-1970s, accounts of the exploits of Allied codebreakers during World War II have focused on successes against the German Enigma cipher systems, the Japanese Foreign Ministry’s machine cipher, and the Imperial Japanese Navy’s codes. The contributions of British cryptanalysts at Bletchley Park to the war against Nazi Germany are well known. The story of the deciphered Japanese diplomatic codes — MAGIC — is also a familiar one and underpins the continuing controversy over American unpreparedness on 7 December 1941 when Japanese naval aircraft attacked Pearl Harbor. Well publicised too are the brilliant feats of US naval cryptanalysts whose decryptions revealed the Japanese navy’s plans at the Battle of the Coral Sea (May 1942) and Midway (June 1942). Numerous authors have re­counted the role of navy cryptanalysts in laying the aerial ambush of Fleet Admiral Yamamoto Isoroku in April 1943. Yet relatively little is known about the US Army’s cryptanalytic assault on the variety of codes or ciphers that Japan’s military forces employed during the Pacific War. Recognition of the scope of US Anny codebreakers’ contributions to victory over Japan is long overdue.KeywordsSecret MessageRegistry GroupUnit CodeCentral BureauTraffic AnalysisThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.