|Attack on Pearl Harbor|
|Approach and attack|
|Possible third wave|
Photograph from a Japanese aircraft of Pearl Harbor including Battleship Row at the beginning of the attack. The explosion in the center is a torpedo strike on the USS West Virginia
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 was a major engagement of World War II. It occurred before a formal declaration of war and before the last part of a 14-part message was delivered to the State Department in Washington, D.C. The Japanese Embassy in Washington had been instructed to deliver it immediately prior to the scheduled time of the attack in Hawaii. The attack, and especially the 'surprise' nature of it, were both factors in changing U.S. public opinion from the isolationist position of the mid-1930s to support for direct participation in the war. Germany's prompt declaration of war, unforced by any treaty commitment to Japan, quickly brought the US into the European Theater as well. The lack by Japan of any formal declaration prior to the attack led President Franklin D. Roosevelt to proclaim "December 7th, 1941 — a date which will live in infamy".
In 1940, under the authority granted by the Export Control Act, the U.S. halted shipments of airplanes, parts, machine tools, and aviation gasoline, which was 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.
Japanese planning staff studied the 1940 British attack on the Italian fleet at Taranto intensively. It was of great use to them when planning their attack on US naval forces in Pearl Harbor.
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 devastating 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., reconquest of the islands had been a given of War Plan Orange in the interwar years.
War between Japan and the United States had been a possibility each nation had been aware of (and developed contingency plans for) since the 1920s, though tensions did not begin to grow seriously until Japan's 1931 invasion of Manchuria. Over the next decade, Japan continued to expand into China, leading to all out war in 1937. In 1940, Japan invaded French Indochina in both an effort to control supplies reaching China, and as a first step to improve her access to resources in Southeast Asia. This move prompted an American embargo on oil exports to Japan, which in turn caused the Japanese to initiate their planned takeover of oil production in the Dutch East Indies. Furthermore, the transfer of the U.S. Pacific Fleet from its previous base in San Diego to its new base in Pearl Harbor was seen by the Japanese military as the U.S. readying itself for a potential conflict between the two countries.
Preliminary planning for an attack on Pearl Harbor to protect the move into the "Southern Resource Area" (the Japanese term for the East Indies and Southeast Asia generally) had begun in very early 1941, under the auspices of Admiral Yamamoto, then commanding Japan's Combined Fleet. He won assent to formal planning and training for an attack from the Imperial Japanese Navy General Staff only after much contention with Naval Headquarters, including a threat to resign his command. Full-scale planning was underway by early spring 1941, primarily by Captain Minoru Genda. Over the next several months, pilots trained, equipment was adapted, and intelligence collected. Despite these preparations, actual approval of the attack plan was not issued by Emperor Showa until November 5, after the third of four Imperial Conferences to consider the matter. Final authorization was not given by the emperor until December 1, after a majority of Japanese leaders advised him the "Hull Note" would "destroy the fruits of the China incident, endanger Manchukuo and undermine Japanese control of Korea." By late 1941 U.S. Pacific bases and facilities had been placed on alert on multiple occasions, with hostilities between the U.S. and Japan expected by many observers. U.S. officials doubted Pearl Harbor would be the first target in any war with Japan, instead expecting the Philippines to be attacked first due to the threat it posed to sea lanes to the south and the erroneous belief that Japan was not capable of mounting more than one major naval operation at a time.
There has been ongoing controversy due to allegations made by conspiracy theorists, military historians and former armed forces personnel that some members of the Roosevelt administration had advance knowledge of the attack, and that this was purposefully ignored in order to gain public and Congressional support for America entering the war on the side of the British Empire and her allies. See Pearl Harbor advance-knowledge debate for more information.
Making battleships the main target was a means of striking at morale, since they were the prestige ships of any navy at the time. Because both Japanese and American strategic thinking and doctrine was derived from the work of Captain Alfred Mahan, which held battleships were decisive in naval warfare, it was also a means of striking at the fighting power of the Pacific Fleet; if it succeeded, it meant the ultimate Pacific battle ("decisive battle", in Japanese Navy thinking), which would inevitably be fought by battleships, would be postponed, if not prevented entirely. With that in mind, Yamamoto intended the Pacific Fleet should be sought and attacked "wherever it might be found in the Pacific". A 14 November 1941 tabletop exercise suggested alert defenders could sink two carriers and damage two more, even with providential weather, which amounted to all the strength Naval General Staff had wanted to allocate to the operation. Nevertheless, Yamamoto pressed ahead.
Japanese confidence in their ability to achieve a short, victorious war also meant other targets in the harbor, especially the Navy Yard, oil tank farms, and Submarine Base, could safely be ignored, since the war would be over before the influence of these facilities would be felt.