The Empire of Japan launched a surprise military attack on the US Pacific Fleet at its naval base at Pearl Harbor in Oahu, Hawaii, on December 7, 1941. At the time, the US was a neutral country in World War II. The air raid on Pearl Harbor, which was launched from aircraft carriers, prompted the US to declare war on Japan the next day. The Japanese military leadership referred to the attack as the Hawaii Operation and Operation AI, and as Operation Z during its planning.
The attack on Pearl Harbor was preceded by months of negotiations between the US and Japan over the future of the Pacific. Japanese demands included that the US end its sanctions against Japan, cease aiding China in the Second Sino-Japanese War, and allow Japan access to the resources of the Dutch East Indies. Japan dispatched its naval attack group on November 26, 1941, just before receiving the Hull note, which stated the US desire that Japan withdraw from China and French Indochina. Isoroku Yamamoto, commander of the Japanese Combined Fleet, planned the attack as a pre-emptive strike on the Pacific Fleet, which had been based at Pearl Harbor since 1940 in order to prevent it from interfering with Japan's planned actions in Southeast Asia. Yamamoto hoped that the strike would enable Japan to make rapid territorial gains and negotiate peace. In addition to Pearl Harbor, over seven hours Japan launched coordinated attacks on the US-held Philippines, Guam, and Wake Island, as well as on the British Empire in Malaya, Singapore, and Hong Kong.
The attacking force, commanded by Chūichi Nagumo, launched its attack at 7:48 a.m. Hawaiian time (6:18 p.m. GMT) on December 7, 1941. The base was struck by 353 fighters, level and dive bombers, and torpedo bombers in two waves launched from six aircraft carriers. Of the eight US battleships present, all were damaged and four were sunk. All but the USS Arizona and the USS Utah were later refloated, and six were returned to service during the war. The Japanese also sank or damaged three cruisers, three destroyers, an anti-aircraft training ship, and a minelayer. More than 180 US aircraft were destroyed. A total of 2,403 Americans were killed and 1,178 others were wounded. Japanese losses totaled 29 aircraft, five midget submarines, and 130 personnel. The three US carriers assigned to Pearl Harbor were at sea at the time, and important base installations, including its oil storage and naval repair facilities, were not attacked.
Japan declared war on the US and the British Empire later that day (December 8 in Tokyo), but the declarations were not delivered until the next day. On December 8, both the United Kingdom and the US declared war on Japan. On December 11, though they had no formal obligation to do so under the Tripartite Pact with Japan, Germany and Italy each declared war on the United States, which responded by declaring war on Germany and Italy. While there were historical precedents for unannounced military action by Japan, the lack of a formal warning and perception that the attack had been unprovoked led US president Franklin D. Roosevelt to famously label December 7, 1941, "a date which will live in infamy". The attack remains the deadliest non-pathological disaster to ever happen in Hawaii, and for nearly 60 years, was the deadliest foreign attack on the US until the September 11 attacks in 2001.
Background
Diplomacy
War between the Empire of Japan and the United States was seen as a possibility since the 1920s. Japan had been wary of American territorial and military expansion in the Pacific and Asia since the late 1890s, followed by the annexation of islands, such as Hawaii and the Philippines, which were close to or within Japan's perceived sphere of influence.
At the same time, Japanese strategic thinkers believed that Japan needed economic self-sufficiency in order to wage modern war. The experiences of World War I had taught the Japanese that modern wars would be protracted, require total mobilization, and create vulnerabilities for trade embargoes and encirclement. As a consequence, Japan needed access to strategically important resources (e.g., iron, oil) that could not be extracted at sufficient levels in the home islands.
Although Japan had begun to take a hostile stance against the United States after the rejection of the Racial Equality Proposal, their relationship was cordial enough to remain trading partners. Tensions did not seriously grow until Japan's invasion of Manchuria in 1931. Over the next decade, Japan expanded into China, leading to the Second Sino-Japanese War in 1937. Japan spent considerable effort trying to isolate China and endeavored to secure enough independent resources to attain victory on the mainland. The "Southern Operation" was designed to assist these efforts. Nevertheless, Japan would still rely heavily on US oil imports, including to Japanese forces in Japan-occupied Manchuria.
In a memorandum dated October 24, 1934, Chief of the Division of Far Eastern Affairs Stanley K. Hornbeck discussed his meeting with Standard Oil New Jersey head Walter C. Teagle to US president Franklin D. Roosevelt. The memo described Teagle as uncooperative with US recommendations, and said that Standard Oil was given special treatment by the Japanese government which made the company less subject to Japan's national business regulation policies than other companies. Hornbeck noted in the memorandum that as a result of Teagle's business dealings with Japan, "the major portion of the petroleum and petroleum products now imported into Japan is of American origin."
Starting in December 1937, events such as the Japanese attack on USS Panay, the Allison incident, and the Rape of Nanjing swung Western public opinion sharply against Japan. The United States unsuccessfully proposed a joint action with the United Kingdom to blockade Japan. In 1938, following an appeal by President Roosevelt, American companies stopped providing Japan with implements of war.
In 1940, Japan invaded French Indochina, attempting to stymie the flow of supplies reaching China. The United States halted shipments of airplanes, parts, machine tools, and aviation gasoline to Japan, which Japan perceived as an unfriendly act. The United States did not stop oil exports, however, partly because of the prevailing sentiment in Washington that given Japanese dependence on American oil, such an action was likely to be considered an extreme provocation.
In mid-1940, President Franklin D. Roosevelt moved the Pacific Fleet from San Diego to Hawaii. He also ordered a military buildup in the Philippines, taking both actions in the hope of discouraging Japanese aggression in the Far East. Because the Japanese high command was mistakenly certain any attack on the United Kingdom's Southeast Asian colonies, including Singapore, would bring the United States into the war, a devastating preventive strike appeared to be the only way to prevent American naval interference. An invasion of the Philippines was also considered necessary by Japanese war planners. The American War Plan Orange had envisioned defending the Philippines with an elite force of 40,000 men; this option was never implemented due to opposition from Douglas MacArthur, who felt he would need a force ten times that size. By 1941, American planners expected to have to abandon the Philippines at the outbreak of war. Late that year, Admiral Thomas C. Hart, commander of the United States Asiatic Fleet, was given orders to that effect.
The United States finally ceased oil exports to Japan in July 1941, following the seizure of French Indochina after the Fall of France, in part because of new American restrictions on domestic oil consumption. Because of this decision, Japan proceeded with plans to take the oil-rich Dutch East Indies. On August 17, Roosevelt warned Japan that America was prepared to take opposing steps if "neighboring countries" were attacked.
Japan and the United States engaged in negotiations during 1941, attempting to improve relations. In the course of these negotiations, Japan offered to withdraw from most of China and Indochina after making peace with the Nationalist government. It also proposed to adopt an independent interpretation of the Tripartite Pact and to refrain from trade discrimination, provided all other nations reciprocated. Washington rejected these proposals. Japanese prime minister Konoe then offered to meet with Roosevelt, but Roosevelt insisted on reaching an agreement before any meeting. The American ambassador to Japan repeatedly urged Roosevelt to accept the meeting, warning that it was the only way to preserve the conciliatory Konoe government and peace in the Pacific. However, his recommendation was not acted upon. The Konoe government collapsed the following month when the Japanese military rejected a withdrawal of all troops from China.
Japan's final proposal, delivered on November 20, offered to withdraw from southern Indochina and to refrain from attacks in Southeast Asia, so long as the United States, United Kingdom, and Netherlands supplied one million U.S. gallons (3.8 million liters) of aviation fuel, lifted their sanctions against Japan, and ceased aid to China. The American counter-proposal of November 26 (November 27 in Japan), the Hull note, required Japan to completely evacuate China without conditions and conclude non-aggression pacts with Pacific powers. On November 26 in Japan, the day before the note's delivery, the Japanese task force left port for Pearl Harbor.
The Japanese intended the attack as a preventive action to keep the United States Pacific Fleet from interfering with their planned military actions in Southeast Asia against overseas territories of the United Kingdom, the Netherlands, and the United States. Over the course of seven hours, there were coordinated Japanese attacks on the American-held Philippines, Guam, Wake Island, Midway Atoll and on the British Empire in Malaya, Singapore, and Hong Kong. From the Japanese point of view, it was seen as a preemptive strike "before the oil gauge ran empty."
Military planning
Preliminary planning for an attack on Pearl Harbor to protect the move into the "Southern Resource Area", the Japanese term for the Dutch East Indies and Southeast Asia generally, began early in 1941 under the auspices of Admiral Isoroku Yamamoto, then commanding Japan's Combined Fleet. He won assent to formal planning and training for an attack from Admiral Osami Nagano, the Chief of 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 Rear Admiral Ryūnosuke Kusaka, with assistance from Commander Minoru Genda and Yamamoto's Deputy Chief of Staff, Captain Kameto Kuroshima. The planners studied the 1940 British air attack on the Italian fleet at Taranto intensively.
Over the next several months, pilots were trained, equipment was adapted, and intelligence was collected. Despite these preparations, Emperor Hirohito did not approve the attack plan until November 5, after the third of four Imperial Conferences called to consider the matter. At first, he hesitated to engage in war but eventually authorized the Pearl Harbor strike despite dissent from certain advisors. 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". Before the attack, he became more involved in military matters, even joining the Conference of Military Councillors, which was considered unusual for him. Additionally, he actively sought more information about the war plans. According to an aide, he openly displayed happiness upon hearing about the success of the surprise attacks.
By late 1941, many observers believed that hostilities between the United States and Japan were imminent. A Gallup poll just before the attack on Pearl Harbor found that 52% of Americans expected war with Japan, 27% did not, and 21% had no opinion. While American Pacific bases and facilities had been placed on alert on many occasions, officials doubted Pearl Harbor would be the first target; instead, they expected the Philippines to be attacked first. This presumption was due to the threat that the air bases throughout that country and the naval base at Manila posed to sea lanes, as well as to the shipment of supplies to Japan from territory to the south. They also incorrectly believed that Japan was not capable of mounting more than one major naval operation at a time.
Objectives
The Japanese attack had several major aims. First, it intended to destroy important American fleet units, thereby preventing the Pacific Fleet from interfering with the Japanese conquest of the Dutch East Indies and Malaya and enabling Japan to conquer Southeast Asia without interference. The leaders of the Imperial Japanese Navy (IJN) subscribed to Alfred Thayer Mahan's "decisive battle" doctrine, especially that of destroying the maximum number of battleships. Second, it was hoped to buy time for Japan to consolidate its position and increase its naval strength before shipbuilding authorized by the 1940 Vinson-Walsh Act erased any chance of victory. Third, to deliver a blow to America's ability to mobilize its forces in the Pacific, battleships were chosen as the main targets, since they were the prestige ships of navies at the time. Finally, it was hoped that the attack would undermine American morale to such an extent that the American government would drop its demands contrary to Japanese interests and seek a peace compromise.
Striking the Pacific Fleet at anchor in Pearl Harbor had two distinct disadvantages: the targeted ships would be in very shallow water, so it would be relatively easy to salvage and possibly repair them, and most of the crews would survive the attack since many would be on shore leave or would be rescued from the harbor. A further disadvantage would prove to be the unexpected absence of all three Pacific Fleet aircraft carriers (Enterprise, Lexington, and Saratoga). Despite these concerns, Yamamoto decided to press ahead.
Japanese confidence in their ability to win a short war meant that other targets in the harbor, especially the navy yard, oil tank farms and submarine base, were left unscathed, since by their thinking the war would be over before the influence of these facilities would be felt.
Approach and attack
On November 26, 1941, Kido Butai, the Mobile Strike Force of the Japanese Navy, departed Hittokapu Bay on Etorofu (now Iterup) Island in the Kuril Islands: six aircraft carriers (Akagi, Kaga, Sōryū, Hiryū, Shōkaku, and Zuikaku), two battleships, three cruisers, 11 destroyers, and eight oilers.
The Japanese plan was for the fleet to steam to a position northwest of Hawaii, and attack Pearl Harbor with aircraft. The attack would consist of about 360 aircraft in two waves. 48 fighter aircraft would remain as defensive combat air patrol (CAP) over the fleet.