@izzythepush,
Ostensibly, and i think this has been well-enough researched, Admiral Nomura, the special envoy in Washington at the time, was unable to decode the message from Tokyo in time to present it in Washington before the attack took place. Ironically, the Americans had broken the Japanese diplomatic codes, and had already decoded that messages, and so knew that Nomura would be presenting a note to the President at about lunch time in Washington. Due to the ineptitude at the Japanese embassy, it was not presented on time--not until sometime after 1:00 p.m., i believe. There were a variety of reasons why Roosevelt, in consultation with General Marshall, Admiral King, the Secretary of War, the Secretary of State and the Secretaries of the Army and the Navy decided to send the war warning message on November 27th. "Purple," the name given to messages decoded from the Japanese diplomatic traffic was one of the major factors. Additionally, the Japanese naval code structure had been broken, so that within a few weeks of the changing of a code, most of it had been decipered. However, the code had been changed ahead of schedule at the beginning of November, 1941, and the special code names for ships and naval stations had not yet been deciphered. Several clues, however, were available. They did not have any information on the six largest carriers (and which were all a part of the First Air Fleet, which had begun steaming for Hawaii on the day the war warning message was written). Although Kimmel, Short and MacArthur were aware of Purple and the Imperial Navy codes, they did not receive transcripts of the intercepts directly. But that should not have mattered.
Nevertheless, all three of them failed to appropriately respond to the war warning message. Kimmel and Short ignored the Martin-Bellinger report, and instituted no regular patrolling to find an enemy fleet. The Martin-Bellinger reprort is chilling in its prediction of what actually happened, especially the conclusion that, due to the ability to avoid detection in shipping lanes, such an attack would very likely come from the north. Finally, Short's almost insane obsession with saboteurs not only made the U. S. Army Air Force on Hawaii unable to respond, it made them sitting ducks.
FDR and his advisors not unreasonably assumed that the commanders in the Pacific would appropriately respond to the war warning message. Another message about the Japanese declaration of war was being prepared when news of the attack reached Washington. One could allege that the boys in Washington should have known the significance of the Purple intercept about Nomura's note--but once again, they reasonably assumed that the men on the scene would already have taken appropriate measures.
So, according to the Japanese plan, the attack would arrive just after Nomura's note was handed in. From the American point of view, it really meant nothing, as FDR, Marshall and King were epecting Kimmel, Short and MacArthur to have already prepared for the eventuality.
