Imperial Japanese Navy - Interwar Years

Interwar Years

In the years before World War II, the IJN began to structure itself specifically to fight the United States. A long stretch of militaristic expansion and the start of the Second Sino-Japanese war in 1937 had exacerbated tensions with the United States, which was seen as a rival of Japan.

The Imperial Japanese Navy was faced, before and during World War II, with considerable challenges, probably more so than any other navy in the world. Japan, like Britain, was almost entirely dependent on foreign resources to supply its economy. To achieve Japan’s expansionist policies, IJN had to secure and protect distant sources of raw material (especially Southeast Asian oil and raw materials), controlled by foreign countries (Britain, France, and the Netherlands). To achieve this goal, she had to build large warships capable of long range.

This was in conflict with Japan's doctrine of "decisive battle" (艦隊決戦, Kantai kessen, which did not require long range), in which IJN would allow the U.S. to sail across the Pacific, using submarines to weaken it, then engage the U.S. Navy in a "decisive battle area", near Japan, after inflicting such attrition. This is in keeping with the theory of Alfred T. Mahan, to which every major navy subscribed before World War II, in which wars would be decided by engagements between opposing surface fleets (as they had been for over 300 years). Following the dictates of Satō (who doubtless was influenced by Mahan), it was the basis for Japan's demand for a 70% ratio (10:10:7) at the Washington Naval Conference, which would give Japan superiority in the "decisive battle area", and the U.S.' insistence on a 60% ratio, which meant parity. Japan, unlike other navies, clung to it even after it had been demonstrated to be obsolete.

It was also in conflict with her past experience. Japan's numerical and industrial inferiority led her to seek technical superiority (fewer, but faster, more powerful ships), qualitative superiority (better training), and aggressive tactics (daring and speedy attacks overwhelming the enemy, a recipe for success in her previous conflicts). She failed to take account of the fact her opponents in the Pacific War did not face the political and geographical constraints of her previous wars, nor did she allow for losses in ships and crews.

Between the wars, Japan took the lead in many areas of warship development:

• In 1921, it launched the Hōshō, the first purpose-designed aircraft carrier in the world to be completed, and subsequently developed a fleet of aircraft carriers second to none.
• In keeping with its doctrine, the Imperial Navy was the first navy in the World to mount 356 mm (14 in) guns (in Kongō), 406 mm (16 in) guns (in Nagato), and then completed the only battleships ever to mount 460 mm (18 in) guns (in the Yamato-class).
• In 1928, she launched the innovative Fubuki-class destroyer, introducing enclosed dual 127 mm (5 in) turrets capable of anti-aircraft fire. The new destroyer design was soon emulated by other navies. The Fubukis also featured the first torpedo tubes enclosed in splinterproof turrets.
• Japan developed the 610 mm (24 in) oxygen fuelled Type 93 torpedo, generally recognized as the best torpedo in the world, to the end of World War II.

By 1921, Japan's naval expenditure reached nearly 32% of the national budget. In 1941, the Imperial Japanese Navy possessed 10 battleships, 10 aircraft carriers, 38 cruisers (heavy and light), 112 destroyers, 65 submarines, and various auxiliary ships.

Japan at times continued to solicit foreign expertise in areas in which the IJN was inexperienced, such as naval aviation. In 1918, Japan invited the French Military Mission to Japan (1918-1919), composed of 50 members and equipped with several of the newest types of airplanes to establish the fundamentals of Japanese naval aviation (the planes were several Salmson 2A2, Nieuport, Spad XIII, two Breguet XIV, as well as Caquot dirigibles). In 1921, Japan hosted for a year and a half the Sempill Mission, a group of British instructors who were able to train and advise the Imperial Japanese Navy on several new aircraft such as the Gloster Sparrowhawk, and on various techniques such as torpedo bombing and flight control.

During the pre-war years, two schools of thought battled over whether the Navy should be organized around powerful battleships, ultimately able to defeat American ones in Japanese waters, or around aircraft carriers. Neither really prevailed, and both lines of ships were developed, with the result neither solution displayed overwhelming strength over the American adversary. A consistent weakness of Japanese warship development was the tendency to incorporate too much armament, and too much engine power, in comparison to ship size (a side-effect of the Washington Treaty), leading to shortcomings in stability, protection and structural strength.