jan 1, 1941 - January: Adm. Yamamoto begins communicating with other Japanese officers about a possible attack on Pearl Harbor.
Jan. 27: Joseph C. Grew, the U.S. ambassador to Japan, wires Washington that he has learned that Japan is planning a surprise attack on Pearl Harbor. No one in Washington believes the information. Most senior American military experts believe the Japanese would attack Manila in the Philippine Islands if war broke out.
