At the start of the Pacific War in December 1941, the Imperial Japanese Navy (IJN) was the third most powerful navy in the world. This was an impressive achievement for an organization which had only been in existence since 1868. The meteoric rise of the IJN was due to a combination of factors, not the least of which was an accepted imperative to modernize in the face of a visible foreign threat, accompanied by able administration and willingness to adapt and innovate, and the assistance of first Great Britain and then other foreign countries. So quickly did the IJN modernize that it was able to defeat China in a war from 1894 to 1895, and then, to the astonishment of the world, vanquish a major European power in the Russo-Japanese War of 1904 to 1905.
The war against Russia culminated in a decisive battle in which the outnumbered Japanese battle fleet prevailed through its superior training and fighting spirit. This became a template for the IJN’s next war, which would be fought against an even more daunting opponent – the United States Navy (USN). The USN had gone from being a hypothetical adversary in 1907 to the only force able to block Japan’s imperial ambitions in 1941. The IJN had spent the entire interwar period preparing for war against the Americans and in 1941 went to war at the height of its powers and even enjoyed a numerical advantage over the USN, which had to devote resources to the Atlantic theater. In 1941, the balance was as favorable as it would ever be for Japan with the IJN honed to a fine edge and the USN not yet reinforced by the ships from its “two-ocean navy” building program which, if realized, would swing the naval balance drastically against the IJN.
The opening of war in December 1941 showed the IJN to be more than a match for the USN and Allied navies for the first six months of conflict. Not only did the IJN possess superior ships in most categories, but the training of their crews under virtual wartime conditions made them decidedly more combat ready than their enemies. As a result the IJN was virtually unchecked during the first phase of the war, during which it accomplished all its objectives for the loss of no ship larger than a destroyer.
The run of Japanese victories was stopped at Coral Sea and Midway in May and June 1942, but the IJN remained a formidable adversary as shown by its ability to outfight the USN during the Guadalcanal campaign from August 1942 until February 1943. This was the true turning point in the Pacific War since it inflicted severe attritional losses on the IJN in ships and aircraft, and, more importantly, in highly trained personnel, for no strategic benefit since the Japanese proved eventually unable to stop the first American offensive of the war. The campaign also indicated another Japanese weakness as tactical excellence proved to be no substitute for lack of strategic insight.
Into 1943, the IJN girded its strength for another decisive battle to turn the tide of the American advance. This occurred first in June 1944 at the Battle of the Philippine Sea, and again a few months later in October in the climactic Battle of Leyte Gulf. Both resulted in catastrophic defeats and by the end of October the IJN was no longer a viable force, which opened the Japanese home islands to the prospect of direct attack. From its initial sweeping victories in 1941 and early 1942 in the Pacific and Indian Oceans, the IJN was reduced in 1945 to mounting effective resistance only with suicide aircraft. The final gesture of committing the superbattleship Yamato, which symbolized the IJN and the Japanese nation, against overwhelming USN air power in April 1945 effectively marked the end of the short life of the IJN.