On January 27th, 1941, Dr. Ricardo Shreiber, the Peruvian envoy in Tokyo, warned Max Bishop, third secretary of the U.S. embassy, that the Japanese were making a war plan involving a surprise attack on Pearl Harbor. This information was sent to the State Department and Naval Intelligence and to Admiral Kimmel in Hawaii.

On September 24th, 1941, a bomb pilot talked in J-19 code (the main Japanese diplomatic code book) from the Japan Naval Intelligence to Japan's Consul General in Honolulu. He requested positions and locations of the U.S. ships so that the bomber planes and torpedo planes could hit their targets. This way there would be no problems of missing, and they wouldn't have to land and restock their bombs. They did not want to give the U.S. forces time to get out of the way and send planes to attack the Japanese.