history

He knew. They all knew.

https://www.archives.gov/publications/prologue/1996/fall/butow.html

“By late November 1941 events were moving at a rapid pace. Even before Stimson dictated his controversial entry for November 25, Secretary Hull had learned, from a "Magic" intercept, that the foreign minister in Tokyo had informed Japan's representatives in Washington that diplomatic efforts to reach what he called "the solution we desire" must be concluded by November 29. They were told: "[This] deadline absolutely cannot be changed." The wording of the very next sentence echoed ominously: "After that, things are automatically going to happened." 22

What things and where? This was the unanswerable question in Washington.

In a message to Winston Churchill, the President revealed that he was aware of the danger from Japan: "We must all be prepared for real trouble, possibly soon."