This provocation was provided by the Japanese attack on Pearl Harbor, Hawaii, where the American Pacific Fleet was based. The attack was planned by Admiral Yamamoto Isoroku, commander-in-chief of Japan's combined fleet. The fleet that sailed to the attack on November 26 was commanded by Admiral Nagumo Chuichi. It had six aircraft carriers, two battleships, three cruisers, 11 destroyers, and about 360 planes. The planes took off when the fleet was about 275 miles (440 kilometers) north of Hawaii. The first wave reached Pearl Harbor at 7:55 a.m. Hawaii time.

The American ships were like sitting ducks in the harbor, and since it was early Sunday morning, many were not fully manned. The battleship Arizona was destroyed, with all hands on board. The California, Nevada, and the West Virginia sank in shallow water. The Oklahoma capsized. Other ships and about 180 airplanes were destroyed or badly damaged. More than 2,300 American military personnel were killed. The next day Roosevelt described the event as a "date which will live in infamy" in a speech to Congress, which promptly declared war on Japan. A few days later Germany and Italy, bound by treaty to Japan, declared war on the United States.

Japan's intention in attacking Pearl Harbor was to disable the American fleet in order to wage a war of conquest across the eastern Pacific without opposition. It nearly worked, but two things went wrong. First, American aircraft carriers were not in port when the attack came, and carriers would prove pivotal in fighting the Pacific War. Second, the Japanese did not bomb the vast oil supply adjacent to the harbor--thus leaving a huge fuel supply for the ships and planes that did survive.

Soon after the attack, U.S. President Franklin D. Roosevelt appointed a commission of inquiry to determine whether negligence had contributed to the success of the Japanese raid on Pearl Harbor. The commission's report found the naval and army commanders of the Hawaiian area, Rear Admiral Husband E. Kimmel and Major General Walter C. Short, guilty of “derelictions of duty” and “errors of judgment”; the two men were subsequently retired. Other later inquiries, however, differed in their conclusions. The Congress of the United States, in an effort to dispose of the controversy, decided on a full, public investigation after the war.

The bipartisan congressional committee opened its investigation in November 1945. Testimony from many people reviewed all known information about the attack on Pearl Harbor. The committee reported its findings in July 1946. It placed the primary blame on General Short and Admiral Kimmel, who, however, were declared guilty only of errors of judgment, and not of derelictions of duty. The committee recommended the unification of the U.S. armed forces, which occurred the following year. 

Today the Pearl Harbor Memorial is located over the remains of the Arizona out in the harbor.

(Dec. 7, 1941), This surprise aerial attack on the U.S. naval base at Pearl Harbor on Oahu Island, Hawaii, by the Japanese precipitated the entry of the United States into World War II. The attack climaxed a decade of worsening relations between the United States and an increasingly expansionist and militaristic 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 Tojo Hideki decided on war.

Admiral 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, the Indonesian Archipelago, and the South Pacific would be open. On November 26 a Japanese fleet, under Vice Admiral 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, a total of about 360 planes were launched.

The first Japanese dive bomber appeared over Pearl Harbor at 7:55 Am (local time). It was followed by 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 very few became airborne. 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 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. President Franklin Roosevelt 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 (Representative Jeannette Rankin of Montana, who had also voted against U.S. entry into World War I).