Thread by @history_dame

80 years- Pearl Harbor
27 Nov 1941
Washington DC:

United States code breakers have been intercepting portions of Japanese diplomatic and military communications issued by the Japanese government through its chain of command.

Thread

The communique decoded imply negotiations with the United States are failing and that after November 30, "things are automatically going to happen."

With other intelligence and locating significant movement, this news caused the Joint Chiefs to issue a notification to Admiral Kimmel and General Walter Short, commander of all Army forces in Hawaii.

The dispatch advised that possible Japanese amphibious forces could be headed to the Malay Peninsula, Thailand, the Philippines, and/or Borneo and that Kimmel and Short should undertake "appropriate defensive measures."

Kimmel noted as significant the absence at Pearl being mentioned as a target of enemy operations.

Japanese efforts at deceptive radio traffic were also significant, which led American intelligence analysts to believe the 1st Air Fleet remained in home waters conducting exercises

2900 nautical miles NW of Oahu:

Kido Butai cuts through the highly choppy seas of the winter North Pacific under complete radio silence.

Communications between vessels-- necessary to maintain formation-- were exclusively by visual signals.

The ships had the keyboards of their teletype radios sealed with wooden slats to prevent even an accidental keystroke from being sent.