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Roosevelt's assertive strategy against Japan was largely a bluff, backed by inadequate armed forces and inadequate funds. Washington theoreticians saw the Philippines as a check to any Japanese move southward. MacArthur overconfidently promised that he would soon have 200,000 Filipinos ready for combat, and the War Department began in the summer of 1941 to ship him the first of a promised 128 new B-17 Flying Fortresses. By April 1942, said Marshall, that would represent "the greatest concentration of heavy-bomber strength anywhere in the world," able to interdict any Japanese assault on Southeast Asia and mount "incendiary attacks to burn up the wood and paper structures of the densely populated Japanese cities."
Perhaps the greatest single cause of American complacency in the Pacific was the fact that the U.S. military's Operation Magic had deciphered Japan's sophisticated Purple diplomatic code in 1940. But that triumph had its drawbacks. U.S. intelligence officials had to sift through so much trivia that they failed to react to some important messages, such as a Tokyo request to its Hawaiian consulate for the exact location of all ships in Pearl Harbor. Also, the code breaking was kept secret even from some key officials. While the British were plugged into Magic, and MacArthur too, Kimmel and Short were not.
Ironically, the Nazis warned the Japanese that their codes might have been broken, but Tokyo refused to believe the Americans were smart enough for such a feat. Just as ironically, while U.S. code breakers knew of the Japanese warships heading for Southeast Asia, Nagumo's radio silence meant that his carriers heading for Pearl Harbor simply disappeared. On Dec. 2, Kimmel's intelligence officer confessed that nothing had been heard from the Japanese carriers for about two weeks.
"What!" said Kimmel. "You don't know where ((they)) are?"
"No, sir, I do not. I think they are in home waters, but I do not know where they are."
"Do you mean to say that they could be rounding Diamond Head, and you wouldn't know it?"
"I hope they would be sighted before now."
And the Americans could intercept but not understand a message Yamamoto sent his fleet on Dec. 2: "Climb Mount Niitaka." That meant "Proceed with the attack."
One thing that the code breaking did tell Washington was Tokyo's answer to Hull's last proposal. Before the original even reached the Japanese envoys, a messenger brought an intercepted version to Roosevelt in his White House study after dinner on Dec. 6. The President read it carefully for about 10 minutes, then said to his closest aide, Harry Hopkins, "This means war."
Roosevelt tried to call Admiral Stark, but he was at a revival of Sigmund Romberg's Student Prince; the President didn't want him paged at the theater lest that cause "undue alarm." When Roosevelt did finally reach him shortly before midnight, the Navy chief said, according to his later recollection, that the message was not "something that required action." After all, Stark testified, warnings had already gone out that Japan was "likely to attack at any time in any direction."