An all-American dispute between the SigInt (Signal Intelligence) services of the US Army and the US Navy had led, as early as September 1940, to the (paradoxical and inefficient) division of roles as follows: on even-numbered days, the SIS (Signal Intelligence Service of the Army) decrypted Japanese diplomatic messages, while the OP-20-G (of the Navy) did so on odd-numbered days. On December 6th, SIS intercepted a message from Tokyo to the Japanese embassy in Washington, communicating the rejection of American terms for resolving the diplomatic crisis. The message was intercepted by the US Navy but sent to SIS for decryption. However, since it was a Saturday, SIS’s civilian translators left their posts at noon. Therefore, the intercepted messages were sent back to the US Navy. Precious hours were lost, and by the time the messages were finally decrypted, Pearl Harbor had already been attacked.
