In the long run, the Japanese attack on Pearl Harbor proved to be a strategie blunder, because it galvanized anti-Japanese sentiment in the United States and brought America's vast industrial capacity into World War II. Winston Churchill said that on the night of Pearl Harbor he slept soundly for the first time in months, because he knew that the United States would now be joining the Allies as a full partner.

In the short run, however, the surprise attack was almost completely successful. In less than an hour, Japanese fighters, bombers, and torpedo bombers sank or damaged six battleships, three cruisers, and three destroyers. The simultaneous raid on Hickham and Wheeler airfields left over 175 planes burning on the runways. Nearly four thousand American soldiers and sailors were killed or wounded. Only the aircraft carriers escaped; at the time of the attack, they were at sea on routine training exercises.

The raid on Pearl Harbor disabled almost half of the United States Navy, paralyzed America's Pacific forces, and served as prologue to a long succession of Japanese victories throughout Southeast Asia and the Pacific. On December 8, Japanese troops landed in Malaya; two days later, the splendid new British battleship Prince of Wales and the battlecruiser Repulse were sunk off the Malayan coast. In rapid succession, the Japanese forced the surrender of Guam, Wake Island, and Hong Kong. On February 15, 1942, the 130,000 British troops manning the supposedly impregnable fortress of Singapore surrendered, after one day of mild resistance.