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

Chapter 2. Intercepted Japanese Diplomatic Messages Reveal a Warning System, 19 November – 28 November 1941

At about quarter after five in the morning of 19 November 1941, a Navy intercept operator at the naval field station at Bainbridge Island, Washington (Station "S"), monitoring 9160 kilocycles, plucked out of the air an eighty-one group message from Foreign Minister Shigenori Togo in Tokyo to the Japanese embassy in Washington, D.C. The operator noted that the message contained an indicator – a reference to the type of key used to encipher the message – that marked the message as intended for a global audience, that is all Japanese diplomatic stations around the world. This indicator was a five-letter group at the beginning of the cipher ...