THIS DAY IN HISTORY: U.S. Intercepted Japanese Message the Day Before Fateful Pearl Harbor Bombing on Dec. 7, 1941
On the night of Dec. 6, 1941, a message to a Japanese delegation in Washington D.C. was intercepted, broken and distributed by the Signal Intelligence Service, or SIS. This message, which would become known as the Fourteen Point Letter, clearly spelled out the Japanese claims that America was trespassing in the Far East.
Source: spacecoastdaily.com