From 1907 onward, IJN leaders identified the United States as the enemy against which preparations had to be made. Yet the Kaigun faced a basic and insoluble problem, namely, Japan's acceptance of the limitation of its navy to three-fifths those of the United States and Great Britain, as agreed at the 1921–1922 Washington Naval Conference. This stance resulted from the conviction of Minister of the Navy Admiral Kato Tomosaburo that the only thing worse for Japan than an unrestricted naval construction race with the United States would be war against that country. Kato believed an unrestricted naval race could only bring the remorseless and irreversible erosion of Japan's position relative to the United States, and Japan therefore had to seek security through peaceful cooperation and diplomatic arrangements rather than through international rivalry and conquest. Kato and others viewed the navy as a deterrent and, in the event of war, a defense; however, they also believed Japan's best interests would be served not by confrontation and conflict with the United States but by arrangements that limited American naval construction relative to Japan and so provided the basis of future American recognition and acceptance of Japan's regional position. The problem was that events unfolded in a manner that forced the IJN into planning for a war that, by its own calculations, it was certain to lose.
The basis of this position was twofold. First, the Kaigun found itself obliged to fight not one but two wars. It would have to confront an American enemy that would seek battle and undertake major amphibious undertakings across the western Pacific to bring the war to Japanese home waters. It would also be obliged to fight a maritime war to defend Japanese shipping and seaborne trade. Losing either would result in Japan's full-scale defeat, no matter whether its navy lost a naval war that left the merchant fleet intact and undiminished or whether Japan was defeated in a maritime war that left its fleet's naval forces unreduced. In the event, Japan and the Kaigun suffered a double defeat, both naval and mercantile.
In a very obvious sense, the maritime defeat was one that could have been predicted. Four Shimushu- or Type A-class escort warships were ordered under the 1937 naval estimates, but none was begun before November 1938, to be completed between June 1940 and March 1941. In December 1941, these four ships were the only purpose-built escorts in service with the IJN, and they all lacked underwater detection gear (sonar).
Quite simply, Japanese industry did not have the capacity to build and service both warships and merchantmen, nor to build both fleet units and escorts. Japan's limited industrial capacity forced it to choose between warships and merchantmen, between building and refitting. Moreover, the Kaigun had no real understanding of trade defense and the principles of convoy. Not until November 1943 did the navy institute general convoy, and lacking sufficient escorts and integrated air defense, this practice merely concentrated targets rather than protecting shipping.
Herein, too, lay the basis of Japan's naval defeat in the Pacific. In order to fight and defeat the American attempt to carry the war across the Pacific, the Kaigun developed the zengen sakusen (all-out battle strategy), a concept that envisaged the conduct of the decisive battle in five phases. Submarines gathered off the Hawaiian Islands would provide timely reports of U.S. fleet movements, and with top surface speeds of 24 knots, they were to inflict a series of nighttime attacks on U.S. formations. It was anticipated they would suffer accumulated losses of one-tenth of strength in this phase and the same in the next, when Japanese shore-based aircraft, especially built for superior range and strike capability, would engage American formations. The enemy would then be subjected to night attack by massed destroyer formations, Japanese battle cruisers and cruisers being used to blast aside escorts: the Japanese anticipated massed scissors attacks using as many as 120 Long Lance torpedoes in a single effort. Thereafter, with U.S. formations losing their cohesion and organization, Japanese carriers would join the battle, employed in separate divisions rather than concentrated, in order to neutralize their opposite numbers. Finally, Japanese battleships would engage the American battle line, in what Japanese planners expected to be the decisive battle. In the 1930s, when these ideas were formulated, the Japanese expected the main battle would take place around the Marianas.
The Kaigun organized its formations and building and refitting programs accordingly. Destroyers featured torpedo armaments, and battleships and cruisers emphasized armament, speed, and armor rather than range. The Yamato-class battleships, at their full displacement of 71,659 tons, carried a main armament of 9 x 18.1-inch guns, an armored belt of 16 inches, and turrets with a maximum of 25.6 inches of armor; they had a top speed of 27.7 knots and a range of 8,600 nautical miles at 19 knots or 4,100 nautical miles at 27 knots. These ships were deliberately conceived as bigger and more formidably armed and protected than any American battleship able to use the Panama Canal. The Japanese quest for qualitative superiority extended through the other classes of warships. As part of this process, the Kaigun developed the famous Long Lance torpedo; land-based and carrier-based aircraft such as the A6M Zero-sen and long-range Betty bomber; and long-range submarines, one type equipped with seaplanes in order to extend scouting range: individually and collectively, these were qualitatively unequaled in 1941 and 1942, and in terms of night-fighting capability in 1941, the Kaigun undoubtedly had no peer.
Despite these apparent advantages, the Japanese naval battle plan represented an inversion of the reality of what was required. By December 1941, the Kaigun had basically secured parity in the Pacific with the United States, with warships, carrier air groups and aircraft, and a pool of trained manpower that were qualitatively probably the best in the world. The problem, however, was that Japan and its armed services lacked the means to fortify the islands of the central and western Pacific. The perimeter along which the Japanese planned to fight the Americans to a standstill largely consisted of gaps. Japan had neither the shipping nor the base organizations needed to transform the island groups into the air bases that were essential to the fleet. The latter, moreover, could not be guaranteed to be permanently ready to meet any American move, which would, by definition, be made in a strength and at a time that all but ensured American victory. Individual Japanese bases or even several bases within a group or neighboring groups could be overwhelmed by an enemy free to take the initiative and choose when to mount offensive operations, a second flaw within the zengen sakusen concept. By 1942, the Kaigun was only prepared to fight the battle it intended to win, and it could only win the battle it intended to fight. Instead, of course, the battle it was called on to fight was not the one for which it had prepared.
The IJN, moreover, faced not one enemy but two. It opened hostilities with a total strength of 10 battleships; 6 fleet and 3 light fleet carriers and 1 escort carrier; 18 heavy and 20 light cruisers; 111 destroyers; and 71 submarines. A token of its future problems lay in the fact that only 1 fleet unit, a destroyer, was not in service on 6 December 1941. But even when it went to war, the Kaigun faced a prewar U.S. Navy that, between May 1942 and November 1943, fought it to a standstill. After that date, the Kaigun faced a wartime U.S. Navy, virtually every ship of which had entered service after Pearl Harbor. The Japanese shipbuilding effort from 1942 to 1944, though substantial, was simply overwhelmed by a truly remarkable American industrial achievement: 18 U.S. fleet carriers to 7 for Japan, 9 light fleet carriers to 4, 77 escort carriers to 4, 8 battleships to 2, 13 heavy and 33 light cruisers to 4 light cruisers, 349 destroyers and 420 destroyer escorts to 90, and 203 submarines to 116. U.S. superiority was not simply numerical: radio, radar, and diversity of weaponry were all areas in which the Kaigun could not match its U.S. enemy but was systematically outclassed as the war entered its second and third years.
During 1943 and 1944, the Americans acquired such overwhelming numerical superiority that the Kaigun was denied not merely any chance of victory but even any means of effective response. Between 26 December 1943 and 24 October 1944, Japanese warships and aircraft destroyed no American fleet units, if U.S. submarines are excluded. The simple truth was not just that the Japanese were prepared to die in order to fight but also that the only way the Japanese could fight was to die.
Events in 1945 conspired to demonstrate the singular ineffectiveness of such a course of action, as Japanese losses between July 1944 and August 1945 reflected both this dilemma and the wider national defeat. In the war overall, the Kaigun lost 1,028 warships of 2,310,704 tons, of which 631 warships of 1,348,492 tons were destroyed in the last 13 months of the war. The wartime losses incurred by the merchant fleet—not the service auxiliaries—told the same story, totaling 1,181.5 merchantmen (there were navy, army, and civilian ships and, occasionally, shared ships, which are here calculated as one half a ship) of 3,389,202 tons, of which 811 vessels of 2,077,249 tons were lost in this same final period, after the Battle of the Philippine Sea. Losses of this order were both the cause and the result of defeat, in practice reducing the Kaigun to no more than an ever less effective coastal defense force.
By August 1945, Japan had been pushed to the edge of final, total, and comprehensive defeat, losing all semblance of strategic mobility. Its industry was in end-run production; its people would have died by the millions from disease and starvation had the war lasted into spring 1946. To all intents and purposes, the Kaigun had by then ceased to exist, as American carrier air groups flew combat air patrol over Japanese airfields. A remarkable American achievement, unparalleled in 400 years, had reduced the Kaigun to impotent irrelevance. States, especially great powers, are rarely defeated by naval power, but in this case, the Kaigun had been entirely powerless to prevent such an outcome. H. P. Willmott
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H. P. Willmott