West Wind Clear: Cryptology and the Winds Message Controversy--A Documentary History

1.2. Japanese Diplomatic and Naval Cryptography and American Code-breaking between the Wars

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It was during World War I that Japan first began to encrypt and encode its diplomatic, military, and naval message traffic. Tokyo's Foreign Ministry, the Gaimusho, started securing its diplomatic messages towards the end of the war. In the decades leading up to the outbreak of general war in the Pacific in late 1941, Japan's diplomats used a variety of manual codes and cipher systems often simultaneously or for overlapping periods. Initially, Japan's diplomatic cryptography emphasized codes over ciphers. The code groups themselves were composed of polygraphic combinations of two, three, four, or five vowels and consonants. These codes often were supplements ...