The attack on Pearl Harbor (or Hawaii Operation, as it was called by the Imperial General Headquarters) was a surprise military strike conducted by the Japanese navy against the United States’ naval base at Pearl Harbor, Hawaii on the morning of Sunday, December 7, 1941, later resulting in the United States becoming militarily involved in World War II. It was intended as a preventive action to keep the U.S. Pacific Fleet from influencing the war Japan was planning to wage in Southeast Asia against Britain, the Netherlands, and the United States. The attack consisted of two aerial attack waves totaling 353 aircraft, launched from six Japanese aircraft carriers.

The attack sank four U.S. Navy battleships (two of which were raised and returned to service late in the war) and damaged four more. The Japanese also sank or damaged three cruisers, three destroyers, and one mine layer, destroyed 188 aircraft, and caused personnel losses of 2,402 killed and 1,282 wounded. The power station, shipyard, maintenance, and fuel and torpedo storage facilities, as well as the submarine piers and headquarters building (also home of the intelligence section) were not hit. Japanese losses were minimal, at 29 aircraft and five midget submarines, with 65 servicemen killed or wounded.

The strike was intended to neutralize the U.S. Pacific Fleet, and hence protect Japan’s advance into Malaya and the Dutch East Indies, where Japan sought access to natural resources such as oil and rubber. Both the U.S. and Japan held long-standing contingency plans for war in the Pacific which were continuously updated as tensions between the two countries steadily increased during the 1930s, with the Japanese expansion into Manchuria and French Indochina greeted by steadily increased levels of embargoes and sanctions from the United States and other nations.

In 1940, under the authority granted by the Export Control Act, the U.S. halted shipments of airplanes, parts, machine tools, and aviation gasoline, and perceived by Japan as an unfriendly act. The U.S. did not stop oil exports to Japan at that time in part because prevailing sentiment in Washington was that such an action would be an extreme step, given Japanese dependence on U.S. oil, and likely to be considered a provocation by Japan.

Following Japanese expansion into French Indochina after the fall of France, the U.S. ceased oil exports to Japan in the Summer of 1941, in part because of new American restrictions on domestic oil consumption. President Franklin D. Roosevelt had earlier moved the Pacific Fleet to Hawaii and ordered a military buildup in the Philippines in the hope of discouraging Japanese aggression in the Far East. As the Japanese high command was (mistakenly) certain any attack on the United Kingdom’s Southeast Asian colonies would bring the U.S. into the war, a preventive strike appeared to be the only way for Japan to avoid U.S. naval interference. An invasion of the Philippines was also considered to be necessary by Japanese war plans, while for the U.S., re-conquest of the islands had been a given of War Plan Orange in the interwar years.

While the attack accomplished its intended objective, it was completely unnecessary. Isoroku Yamamoto, who conceived the original plan, didn’t know that the U.S. Navy had decided as far back as 1935 to abandon ‘charging’ across the Pacific towards the Philippines in response to an outbreak of war (in keeping with the evolution of Plan Orange). The U.S. instead adopted “Plan Dog” in 1940, which emphasized keeping the Imperial Japanese Navy out of the eastern Pacific and away from the shipping lanes to Australia while the U.S. concentrated on defeating Nazi Germany.

The attack was an important engagement of World War II. Unintentionally occurring before a formal declaration of war (which had been scheduled to be delivered shortly prior to the attack beginning), it pushed U.S. public opinion from isolationism to the acceptance of participation in the war being unavoidable. The lack of warning led Roosevelt to call it “a date which will live in infamy.”