President Roosevelt and Secretary of State Cordell Hull knew a Japanese attack was imminent. Having received intelligence reports of intercepted coded messages from Tokyo to the Japanese ambassador in the United States, the president anticipated Japanese reprisals for his government's refusal to reverse economic sanctions and embargoes against Japan. The Roosevelt administration had remained firm in its demand that the Japanese first withdraw from China and French Indochina, which it had invaded in 1937 and July 1941, respectively, and renounce its alliance with fascist Germany and Italy.
But Japan refused, demanding that the United States first end the embargo on oil shipments vital for Tokyo's war machine. Although negotiations between the two nations continued up to the very last minute, Roosevelt was aware of a secret November 25 deadline, established by Tokyo, that confirmed military action on the part of the Japanese should they not received satisfaction from the negotiations. While forewarned, Washington could not pinpoint the time or place of an attack.
Despite initially objecting to war with America, Admiral Isoruku Yamamoto believed that if Prime Minister Hideki Tojo was determined to go to war, it was Japan who had to make a preemptive strike. Yamamoto studied the devastating November 1940 British attack against the Italian fleet at Taranto, and planned and led the sneak attack against the United States. Approximately 360 Japanese warplanes were launched from six aircraft carriers, reinforced by battleships, cruisers, and destroyers. The first dive-bomber was spotted over Pearl Harbor at 7:55 a.m. Hawaii time. It was followed by 200 aircraft, which decimated the American ships anchored there, most of which were only lightly manned because it was Sunday morning. Among the 18 U.S. ships destroyed, sunk, or capsized were the Arizona, Virginia, California, Nevada, and West Virginia. More than 180 planes were destroyed on the ground and another 150 were damaged (leaving but 43 operational). American casualties totaled more than 3,400, with more than 2,400 killed (1,000 on the Arizona alone). The Japanese lost fewer than 100 men.
In the short term, the Japanese goal of crippling U.S. naval strength in the Pacific, and thereby giving Tokyo free reign to gobble up more of Southeast Asia and the South Pacific in its dream of imperial expansion, was successful. But the war had only just begun.