Japan focused on assets such as the Kaga to counter perceived oppression by the United States—which adapted.
Between World Wars I and II, carrier aviation emerged as the key component of Japan’s strategy to intercept and quickly annihilate the U.S. Pacific Fleet. Even though the Imperial Japanese Navy (IJN) had a larger, more effective force at the onset of the Pacific war, the U.S. Navy inflicted devastating carrier losses on Japan in 1942 at Coral Sea and Midway. Japan’s ultimate defeat was due in part to how quickly the United States energized its industrial capacity and how effectively the U.S. Navy adapted strategy and tactics from lessons learned earlier in the war.
Between 1917 and 1920, the IJN had secretly obtained the details of War Plan Orange, the U.S. blueprint for fighting a possible war with Japan, and by 1918, Tokyo viewed the United States as its most probable and formidable future naval adversary. Based on War Plan Orange, the Japanese Naval General Staff calculated that the IJN needed to be at least 70 percent of the size of the U.S. Navy to counter U.S. naval forces attacking from the western Pacific. A quick Japanese victory was necessary because a drawn-out conflict would exhaust the nation’s resources.
However, the treaty that emerged from the 1921–22 Washington Naval Conference had limited the size of the IJN to only 60 percent of the size of the U.S. and British navies, following the stipulated ratio of 5:5:3. While contrary to the design of its own war plans, Japan’s agreement to the Washington treaty in 1922 demonstrated its desire to ease interwar tensions with the United States and Great Britain, while also revealing the conflicting attitudes of Japan’s civilian-controlled Navy Ministry and its military-led Naval General Staff. Still, many Japanese, especially the Naval General Staff, viewed the stipulated ratio as yet another example of excessive U.S. influence and oppression, and this motivated the IJN to find other ways to overcome its disadvantages in naval power.
Throughout the 1920s and early 1930s, Japan was able to keep up with U.S. carrier production by converting two battle cruisers to 30,000-ton aircraft carriers and building several smaller 8,000- to 10,000-ton carriers that were not restricted by the treaty. In 1936 Japan withdrew from the Washington treaty, thus removing any restrictions on IJN strength. Soon Japan had surpassed the United States in both carrier shipbuilding and carrier-aircraft technological capability, improving on the effectiveness of carrier-launched fighters and torpedo bombers by testing and building planes that could achieve longer ranges and faster speeds and dominate in night-fighting tactics. IJN pilot proficiency in night-fighting tactics exemplifies the effectiveness of its training doctrine.
Meanwhile, the United States decided to remain bound by treaty restrictions, and, as Samuel Eliot Morison explains in The Two-Ocean War, the size of the Navy was “allowed to fall so low that there was a vast gap to be filled before even treaty strength could be attained.” But Japan’s proactive military understood and cooperated with the nation’s industrial system, which enabled massive construction of aircraft carriers, technological development of carrier-launched aircraft, and an increase in the overall strength of Japan’s carrier aviation force. In addition, as Geoffrey Till notes in “Adopting the Aircraft Carrier,” Japan’s aggressive and realistic training doctrine reinforced carrier aviation strategy and tactics that had been learned during the 1930s war with China, when Japan discovered not only carrier aviation’s long-distance power-projection capability but also “the value of long-range fighter escorts and high performance aircraft.” Its training doctrine mandated regular live fleet exercises with “ruthless realism,” explains Till. Through repetition and near-real warlike conditions, the IJN honed its war-fighting skills and derived further lessons that were applied to live training and war plans. The Japanese Naval War College used wargame analysis to assess the strategies and tactics of carrier aviation that later influenced the decision to attack Pearl Harbor.
Overall, by the time World War II broke out, Japan had positioned itself better than the United States for naval combat using carrier aviation. Its prewar attitudes and doctrine had made it more successful in the development, innovation, and advancement of this technology. When Japan attacked Pearl Harbor on 7 December 1941, it had 11 aircraft carriers in service, whereas the United states had only seven. With a sizable and superior carrier force and naval doctrine tested by combat and supported by thorough training, pre–World War II Japan seemed well poised to take on the United States in a quick and decisive battle at sea in the western Pacific.
Sadao Asada, “The Revolt against the Washington Treaty: The Imperial Japanese Navy and Naval Limitation, 1921–1927,” H200: Military Innovation in Peace and War Syllabus and Book of Readings (Fort Leavenworth, KS: U.S. Army Command and General Staff College, 2008).
Scot MacDonald, “Evolution of Aircraft Carriers: The Japanese Developments,” Naval Aviation News, October 1962, http://history.navy.mil/download/car-7.pdf.
Samuel Eliot Morison, The Two-Ocean War: A Short History of the United States in the Second World War (Annapolis, MD: Naval Institute Press, 1963), 20.
Peter Paret, ed., Makers of Modern Strategy from Machiavelli to the Nuclear Age (Princeton: Princeton University Press, 1986).
Craig L. Symonds, The Naval Institute Historical Atlas of the U.S. Navy (Annapolis, MD: Naval Institute Press, 1995).
Geoffrey Till, “Adopting the Aircraft Carrier: The British, American, and Japanese Case Studies,” in Williamson Murray and Allan R. Millett, eds., Military Innovation in the Interwar Period (Cambridge: Cambridge University Press, 1996), 221, 197.