Imperial Japanese Navy in World War II

The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the third most powerful navy in the world. During the first six months of the war, the Navy was undefeated in every battle. However, after a series of defeats it lost control of the Western Pacific and collapsed by the end of the war. The naval air service was one of the most potent air forces in the world before its destruction in World War II.

At the beginning of the Pacific War, the strategy of the Imperial Japanese Navy was underpinned by several key assumptions. The most fundamental was that, just as the Russo-Japanese war had been decided by the naval Battle of Tsushima (May 27–28, 1905), the war against the United States would be decided by a single decisive naval battle, or Kantai Kessen. This great naval clash would be determined by the big guns aboard battleships, and this conviction was shared by both the Japanese and the American naval leaders alike. All other arms of the navy were to be dedicated to supporting the battleships when they met the Americans in battle. The Japanese assumed that at the start of any conflict, they would quickly seize the largely unprotected American-held Philippines. This would force the United States to undertake a drive across the Pacific to retake them. Consequently, the great decisive clash would take place somewhere in the western Pacific where the Japanese decided was right area to stop the American advance.

It was also clear to the Japanese that in order to win the decisive battle they would have to make up for their numerical disadvantage. The Japanese acknowledged that they would never have the industrial capacity to create a navy that was equal in size to the United States, however, as they were planning on fighting a defensive war, they calculated that they had to have only 70 percent of the strength of the United States Navy to be in a position to achieve victory. This assumption was built on two pillars, both became driving forces in Japanese naval construction, tactical development, and training between the wars. The first was that the Japanese would had to have the weapons and tactics to inflict severe attrition on the US Pacific Fleet before the decisive battle, which would bring the Japanese to at least parity. Once at rough parity, Japanese naval units with superior speed and capable of hitting at ranges beyond the reach of the Americans and crewed by expertly trained personnel, would win the day.

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