(Dec. 7, 1941), surprise aerial attack on the U.S. naval base at Pearl Harbor on Oahu Island, Hawaii, by the Japanese that precipitated the entry of the United States into World War II. The attack climaxed a decade of worsening relations between the United States and Japan. Japan's invasion of China in 1937, its subsequent alliance with the Axis powers (Germany and Italy) in 1940, and its occupation of French Indochina in July 1941 prompted the United States to respond that same month by freezing Japanese assets in the United States and declaring an embargo on petroleum shipments and other vital war materials to Japan. By late 1941 the United States had severed practically all commercial and financial relations with Japan. Though Japan continued to negotiate with the United States up to the day of the Pearl Harbor attack, the government of Prime Minister Tōjō Hideki decided on war.

Adm. Yamamoto Isoroku, the commander in chief of Japan's Combined Fleet, had planned the attack against the U.S. Pacific Fleet with great care. Once the U.S. fleet was out of action, the way for the unhindered Japanese conquest of all of Southeast Asia and the Indonesian Archipelago would be open. On November 26 a Japanese fleet, under Vice Adm. Nagumo Chuichi and including 6 aircraft carriers, 2 battleships, 3 cruisers, and 11 destroyers, sailed to a point some 275 miles (440 km) north of Hawaii. From there, about 360 planes in total were launched.

The first Japanese dive bomber appeared over Pearl Harbor at 7:55 AM (local time). It was part of a first wave of nearly 200 aircraft, including torpedo planes, bombers, and fighters. The reconnaissance at Pearl Harbor had been lax; a U.S. Army private who noticed this large flight of planes on his radar screen was told to ignore them, since a flight of B-17s from the United States was expected at that time. The anchored ships in the harbour made perfect targets for the Japanese bombers, and since it was Sunday morning (a time chosen by the Japanese for maximum surprise) they were not fully manned. Similarly, the U.S. military aircraft were lined up on the airfields of the Naval Air Station on Ford Island and adjoining Wheeler and Hickam Fields to guard against sabotage, and many were destroyed on the ground by Japanese strafing. Most of the damage to the battleships was inflicted in the first 30 minutes of the assault. The Arizona was completely destroyed and the Oklahoma capsized. The California, Nevada, and West Virginia sank in shallow water. Three other battleships, three cruisers, three destroyers, and other vessels were also damaged. More than 180 aircraft were destroyed. U.S. military casualties totaled more than 3,400, including more than 2,300 killed. The Japanese lost from 29 to 60 planes, five midget submarines, perhaps one or two fleet submarines, and fewer than 100 men.

The Pearl Harbor attack severely crippled U.S. naval (United States Navy, The) and air strength in the Pacific. However, the three aircraft carriers attached to the Pacific Fleet were not at Pearl Harbor at the time and thus escaped. Of the eight battleships, all but the Arizona and Oklahoma were eventually repaired and returned to service, and the Japanese failed to destroy the important oil storage facilities on the island. The “date which will live in infamy,” as U.S. Pres. Franklin D. Roosevelt (Roosevelt, Franklin D.) termed it, unified the U.S. public and swept away any earlier support for neutrality. On December 8 Congress declared war on Japan with only one dissenting vote (Rep. Jeannette Rankin of Montana, who had also voted against U.S. entry into World War I).