On December 7, 1941, without any warning, 360 Japanese aircraft bombed the American naval base at Pearl Harbor, Hawaii. The surprise attack, masterminded by the Japanese admiral Isoroku Yamamoto, was devastating for the US Pacific Fleet. Four battleships sunk, four more were disabled; eleven other ships were sunk or critically damaged; 188 aircraft were destoyed on the ground at Hickham Field; 2,330 servicemen and 100 civilians were killed. The American defenders scrambled to their posts, and shot down 29 Japanese planes, killing 64.

The attack on Pearl Harbor was timed to coincide with the Japanese landings on Hong Kong, Malaya and Thailand and air bombings on American bases on the Philippines, Guam and Wake and Midway Islands.

The following day, President Franklin D Roosevelt informed his people of the bombing, and condemned December 7, 1941 as a day of infamy. Outraged by the bombing, the USA, Britain and nine Latin American states declared war on Japan. On December 11, Hitler rashly declared war on the United States (which until then had remained neutral in Europe), thus ensuring the eventual defeat of the Axis Powers. The bombing had a dramatic effect on the eventual outcome of the war, as it brought much-needed US resources to the aid of the Allies.