While no one can excuse Japan's belligerence in those days, it is also true that our government provoked that country in various ways, freezing her assets in America; closing the Panama Canal to her shipping; progressively halting vital exports to Japan until we finally joined Britain in an all-out embargo; sending a hostile note to the Japanese ambassador implying military threats if Tokyo did not alter its Pacific policies; and on November 26th just 11 days before the Japanese attack delivering an ultimatum that demanded, as prerequisites to resumed trade, that Japan withdraw all troops from China and Indochina, and in effect abrogate her Tripartite Treaty with Germany and Italy.
After meeting with President Roosevelt on October 16, 1941, Secretary of War Henry Stimson wrote in his diary: We face the delicate question of the diplomatic fencing to be done so as to be sure Japan is put into the wrong and makes the first bad move. Overt move. On November 25th, the day before the ultimatum was sent to Japan's ambassadors, Stimson wrote in his diary: The question was how we should manoeuver them [the Japanese] into the position of firing the first shot.
The bait offered Japan was our Pacific Fleet. In 1940, Admiral J.O. Richardson, the fleet's commander, flew to Washington to protest FDR's decision to permanently base the fleet in Hawaii instead of its normal berthing on the U.S. West Coast. The admiral had sound reasons: Pearl Harbor was vulnerable to attack, being approachable from any direction; it could not be effectively rigged with nets and baffles to defend against torpedo planes; and in Hawaii it would be hard to supply and train crews for his undermanned vessels. Pearl Harbor also lacked adequate fuel supplies and dry docks, and keeping men far from their families would create morale problems. The argument became heated. Said Richardson: I came away with the impression that, despite his spoken word, the President was fully determined to put the United States into the war if Great Britain could hold out until he was re-elected.
Richardson was quickly relieved of command. Replacing him was Admiral Husband E. Kimmel. Kimmel also informed Roosevelt of Pearl Harbor's deficiencies, but accepted placement there, trusting that Washington would notify him of any intelligence pointing to attack. This proved to be misplaced trust. As Washington watched Japan preparing to assault Pearl Harbor, Admiral Kimmel, as well as his Army counterpart in Hawaii, General Walter C. Short, were completely sealed off from the information pipeline.
PRIOR KNOWLEDGE
One of the most important elements in America's foreknowledge of Japan's intentions was our government's success in cracking Japan's secret diplomatic code known as Purple. Tokyo used it to communicate to its embassies and consulates, including those in Washington and Hawaii. The code was so complex that it was enciphered and deciphered by machine. A talented group of American cryptoanalysts broke the code in 1940 and devised a facsimile of the Japanese machine. These, utilized by the intelligence sections of both the War and Navy departments, swiftly revealed Japan's diplomatic messages. The deciphered texts were nicknamed Magic.
Copies of Magic were always promptly delivered in locked pouches to President Roosevelt, and the secretaries of State, War, and Navy. They also went to Army Chief of Staff General George Marshall and to the Chief of Naval Operations, Admiral Harold Stark. However, although three Purple decoding machines were allotted to Britain, none were sent to Pearl Harbor. Intercepts of ciphered messages radioed between Tokyo and its Honolulu consulate had to be forwarded to Washington for decrypting. Thus Kimmel and Short, the Hawaiian commanders, were at the mercy of Washington for feedback. A request for their own decoding machine was rebuffed on the grounds that diplomatic traffic was of insufficient interest to soldiers.
How untrue that was! On October 9, 1941, the War Department decoded a Tokyo-to-Honolulu dispatch instructing the Consul General to divide Pearl Harbor into five specified areas and to report the exact locations of American ships therein.
There is nothing unusual about spies watching ship movements but reporting precise whereabouts of ships in dock has only one implication. Charles Willoughby, Douglas MacArthur's chief of intelligence later wrote that the "reports were on a grid system of the inner harbor with coordinate locations of American men of war A coordinate grid is the classical method for pinpoint target designation; our battleships had suddenly become targets." This information was never sent to Kimmel or Short.
Additional intercepts were decoded by Washington, all within one day of their original transmission:
November 5th: Tokyo notified its Washington ambassadors that November 25th was the deadline for an agreement with the U.S.
November 11th: They were warned, The situation is nearing a climax, and the time is getting short.
November 16th: The deadline was pushed up to November 29th. The deadline absolutely cannot be changed, the dispatch said. After that, things are automatically going to happen.
November 29th (the U.S. ultimatum had now been received): The ambassadors were told a rupture in negotiations was inevitable, but that Japan's leaders do not wish you to give the impression that negotiations are broken off.
November 30th: Tokyo ordered its Berlin embassy to inform the Germans that the breaking out of war may come quicker than anyone dreams.
December 1st: The deadline was again moved ahead. To prevent the United States from becoming unduly suspicious, we have been advising the press and others that the negotiations are continuing.
December 1st-2nd: The Japanese embassies in non-Axis nations around the world were directed to dispose of their secret documents and all but one copy of their codes. (This was for a reason easy to fathom when war breaks out, the diplomatic offices of a hostile state lose their immunity and are normally overtaken. One copy of code was retained so that final instructions could be received, after which the last code copy would be destroyed.) An additional warning came via the so-called Winds message. A November 18th intercept indicated that, if a break in U.S. relations were forthcoming, Tokyo would issue a special radio warning. This would not be in the Purple code, as it was intended to reach consulates and lesser agencies of Japan not equipped with the code or one of its machines. The message, to be repeated three times during a weather report, was 'Higashi no kaze ame', meaning East wind, rain.'East wind 'signified the United States; 'rain' signified diplomatic split, in effect, war.