WWII history

Pearl Harbor: Hawaii Was Surprised; FDR Was Not

One of the most important elements in America's foreknowledge of Japan's intentions was our government's success in cracking Japan's secret diplomatic code known as "Purple." Tokyo used it to communicate to its embassies and consulates, including those in Washington and Hawaii. The code was so complex that it was enciphered and deciphered by machine. A talented group of American cryptoanalysts broke the code in 1940 and devised a facsimile of the Japanese machine. These, utilized by the intelligence sections of both the War and Navy departments, swiftly revealed Japan's diplomatic messages. The deciphered texts were nicknamed "Magic."

Copies of Magic were always promptly delivered in locked pouches to President Roosevelt, and the secretaries of State, War, and Navy. They also went to Army Chief of Staff General George Marshall and to the Chief of Naval Operations, Admiral Harold Stark. However, although three Purple decoding machines were allotted to Britain, none was sent to Pearl Harbor. Intercepts of ciphered messages radioed between Tokyo and its Honolulu consulate had to be forwarded to Washington for decrypting. Thus Kimmel and Short, the Hawaiian commanders, were at the mercy of Washington for feedback. A request for their own decoding machine was rebuffed on the grounds that diplomatic traffic was of insufficient interest to soldiers.