The Attack on Pearl Harbor
December 7, 1941

Nationalistic and militaristic fervor in Imperial Japan and a strong belief in Japan's destiny and divine right to rule all of Southeast Asia brought Japan and the United States into increasing diplomatic confrontation throughout the 1930s. Compounding the matter was a bloody undeclared war the Japanese were waging in China and the weakening of European control in Asian colonies as a result of the Second World War. The signing of the Tripartite Pact in September 1940, which allied Japan with Germany and Italy, aggravated tensions between the United States and Japan as the latter nation joined the Axis Powers. When Japan seized a major portion of Southeast Asia under agreement with Vichy France, the administration of President Franklin D. Roosevelt was moved to action. Already outraged by Japanese aggression in China, the Roosevelt administration introduced economic sanctions to make its point clear: The United States would not facilitate Japan's expansion into the Pacific, just as it opposed German expansion in Europe. An American embargo cut off shipments of scrap steel, raw materials, oil and high-octane gasoline, while freezing Japanese financial assets in the United States. The Japanese, having only a six-month supply of strategic fuel available for its armed forces, felt the only choice was to initiate the conquest of Southeast Asia, which meant inevitable war with America, Britain, and the Netherlands. Japan had seen the United States expand its naval authority in the Pacific in the late 1930s. The bolstering of defenses in the Philippines, Hawaii, Guam, Midway and Wake Island, as well as stationing the United States Pacific Fleet at Pearl Harbor, made America the first priority for a Japanese attack.

Admiral Isoruko Yamamoto, chief architect of the attack on Pearl Harbor. U.S. Naval Historical Center photo NH63430.

Fearing that the U.S. Pacific Fleet would pose a formidable obstacle to Japanese conquest of Southeast Asia, Admiral Isoruko Yamamoto, the Commander-in-Chief of the Japanese Combined Fleet, visualized a bold attack on the Pacific Fleet while it lay at anchor at Pearl Harbor. Such a "surprise strategical" attack, bold and daring in its execution, would secure the Pacific and initiate the war, following in the tradition of the Japanese naval victory over the Russians at Port Arthur in 1904 and the opening maneuvers in Japan's invasion of China. Although nationalistic and militaristic pride was driving Japan inexorably toward war with the United States, some military leaders were concerned about the long-range implications of a protracted war with an industrial giant. Yamamoto expressed doubt, apprehension and disgust over Japan's headlong push toward conflict. In January 1941 he wrote to Ryoichi Sasakawa, who was the president of Japan's rightist nationalistic organization Kokusai Domei and one of Yamamoto's staunch supporters:

. . . if there should be a war between Japan and America, then our aim, of course, ought not to be Guam or the Philippines, nor Hawaii or Hong Kong, but a capitulation at the White House, in Washington itself. I wonder whether the politicians of the day really have the willingness to make sacrifices, and the confidence, that this would entail?

Thus the admiral, who was about to initiate the opening attack of the war, revealed his personal attitude. Although he was reluctant to push toward war, he possessed a strong sense of duty. With Japanese policy indicating that war was now inevitable, Yamamoto took a hard look at the navy and Japan's chances, noting he expected to "run wild" for six months, with the outcome after that up in the air. In order to hit U.S. forces so hard that America would seek a quick peace, Yamamoto explained to Navy Minster Koshiro Oikawa, "We should do our very best . . . to decide the fate of the war on the very first day." He described his operational plan to attack Pearl Harbor.

The plan had been mentioned before. In the spring of 1940 Japan's air fleet had conducted aerial torpedo exercises under the watchful eyes of Yamamoto and Rear Admiral Shigeru Fukudome, head of the first division of the naval general staff. In passing conversation, almost in a whisper, Yamamoto had said, "I wonder if an aerial attack can't be made at Pearl Harbor?" (Prange 1981:14). Even then, the thought was not new. Exercises by both countries had played out such a scenario, but both Japan and the United States believed an aerial torpedo attack on Pearl Harbor was impossible. The actual plan of operation, formulated by a young tactical genius in aerial warfare, Commander Minoru Genda, was agreed to after months of internal dissension among the ranks of command in the Japanese navy. When negotiations with the United States were deemed unsatisfactory to the Japanese government of Prime Minister Hideki Tojo, official blessing was sought for the "Hawaii Operation." It was given on September 6, 1941, at an Imperial Conference. Japan was committed to war.

The First Air Fleet had held maneuvers for almost a year, and the results were promising. Under the direction of Commander Mitsuo Fuchida, who would lead the air assault on Pearl Harbor, the "impossible" task of an aerial torpedo attack was made possible. Conventional aerial torpedoes plunged to more than 100 feet in depth and ran a long distance to arm. The 45-foot average depth of Pearl Harbor and the short runs necessary to sink ships there were dealt with by adding wooden fins to the torpedoes, altering the arming devices, and by training in simulated conditions.

The Japanese carrier Kaga pitches in heavy sea in the North Pacific in early December 1941, en route to the attack on Pearl Harbor. This is a still frame from a Japanese motion picture captured in 1943. U.S. Naval Historical Center photo NH75483

A task force of 32 vessels -- particularly the carriers Akagi, Hiryu, Soryu, Kaga, Zuikaku and Shokaku --was dubbed the "Kido Butai" (Strike Force). Secretly assembling on Tankan Bay in Northern Japan, the force was placed under the direct command of Vice Admiral Chuichi Nagumo. At 6:00 a.m. on November 26, 1941, the Japanese fleet weighed anchor and slipped out to sea for Hawaii. In planning the operation, the northern approach to Hawaii had been selected even though the weather and seas would be rough. The winter storms would mask the Japanese fleet and lessen the chances of encountering the enemy while on the high seas. A screening force of submarines traveled 200 miles ahead, and as the fleet approached Hawaii, it received up-to-date reports from agents on Oahu as well as the submarines, which finally were picketed around the islands. On December 2 a coded message arrived in Tokyo: "Climb Mt. Nitaka." This pre-arranged message signaled the final decision to wage war. The fleet was to press forward and attack on Sunday, December 7, 1941, Hawaii time.

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