Imperial Japanese Navy

No. 6 Odaiba battery, one of the original Edo-era battery islands. These batteries are defensive structures built to withstand naval intrusions.

For more than 200 years, beginning in the 1640s, the Japanese policy of seclusion ("sakoku") forbade contacts with the outside world and prohibited the construction of ocean-going ships on pain of death.[11] Contacts were maintained, however, with the Dutch through the port of Nagasaki, the Chinese also through Nagasaki and the Ryukyus and Korea through intermediaries with Tsushima. The study of Western sciences, called "rangaku" through the Dutch enclave of Dejima in Nagasaki led to the transfer of knowledge related to the Western technological and scientific revolution which allowed Japan to remain aware of naval sciences, such as cartography, optics and mechanical sciences. Seclusion, however, led to the loss of any naval and maritime traditions the nation possessed.[5]

Apart from Dutch trade ships, no other Western vessels were allowed to enter Japanese ports. A notable exception was during the Napoleonic wars when neutral ships flew the Dutch flag. Frictions with the foreign ships, however, started from the beginning of the 19th century. The Nagasaki Harbour Incident involving HMS Phaeton in 1808, and other subsequent incidents in the following decades, led the shogunate to enact an Edict to Repel Foreign Vessels. Western ships, which were increasing their presence around Japan due to whaling and the trade with China, began to challenge the seclusion policy.

The Morrison Incident in 1837 and news of China's defeat during the Opium War led the shogunate to repeal the law to execute foreigners, and instead to adopt the Order for the Provision of Firewood and Water. The shogunate also began to strengthen the nation's coastal defenses. Many Japanese realized that traditional ways would not be sufficient to repel further intrusions, and western knowledge was utilized through the Dutch at Dejima to reinforce Japan's capability to repel the foreigners; field guns, mortars, and firearms were obtained, and coastal defenses reinforced. Numerous attempts to open Japan ended in failure, in part to Japanese resistance, until the early 1850s.

During 1853 and 1854, American warships under the command of Commodore Matthew Perry, entered Edo Bay and made demonstrations of force requesting trade negotiations. After two hundred years of seclusion, the 1854 Convention of Kanagawa led to the opening of Japan to international trade and interaction. This was soon followed by the 1858 Treaty of Amity and Commerce and treaties with other powers.

• 
  Replica of the Japanese-built 1613 galleon San Juan Bautista, in Ishinomaki
• 
  Painting of a 17th-century Red Seal Ship of the Araki clan, sailing out of Nagasaki for Annam (Vietnam)
• 
  The sailing frigate Shōhei Maru (1854) was built from Dutch technical drawings.

As soon as Japan opened up to foreign influences, the Tokugawa shogunate recognized the vulnerability of the country from the sea and initiated an active policy of assimilation and adoption of Western naval technologies.[12] In 1855, with Dutch assistance, the shogunate acquired its first steam warship, Kankō Maru, and began using it for training, establishing a Naval Training Center at Nagasaki.[12]

Samurai such as the future Admiral Enomoto Takeaki (1836–1908) was sent by the shogunate to study in the Netherlands for several years.[12] In 1859 the Naval Training Center relocated to Tsukiji in Tokyo. In 1857 the shogunate acquired its first screw-driven steam warship Kanrin Maru and used it as an escort for the 1860 Japanese delegation to the United States. In 1865 the French naval engineer Léonce Verny was hired to build Japan's first modern naval arsenals, at Yokosuka and Nagasaki.[13]

The shogunate also allowed and then ordered various domains to purchase warships and to develop naval fleets,[14] Satsuma, especially, had petitioned the shogunate to build modern naval vessels.[12] A naval center had been set up by the Satsuma domain in Kagoshima, students were sent abroad for training and a number of ships were acquired.[12] The domains of Chōshū, Hizen, Tosa and Kaga joined Satsuma in acquiring ships.[14] These naval elements proved insufficient during the Royal Navy's Bombardment of Kagoshima in 1863 and the Allied bombardments of Shimonoseki in 1863–64.[12]

By the mid-1860s the shogunate had a fleet of eight warships and thirty-six auxiliaries.[14] Satsuma (which had the largest domain fleet) had nine steamships,[15] Choshu had five ships plus numerous auxiliary craft, Kaga had ten ships and Chikuzen eight.[15] Numerous smaller domains also had acquired a number of ships. However, these fleets resembled maritime organizations rather than actual navies with ships functioning as transports as well as combat vessels;[12] they were also manned by personnel who lacked experienced seamanship except for coastal sailing and who had virtually no combat training.[12]

• 
  The screw-driven steam corvette Kanrin Maru, Japan's first screw-driven steam warship, 1857
• 
  The gunboat Chiyoda, was Japan's first domestically built steam warship. It was completed in May 1866.[16]
• 
  The French-built ironclad warship Kōtetsu (ex-CSS Stonewall), Japan's first modern ironclad, 1869

The Naval Battle of Hakodate, May 1869; in the foreground, wooden paddle steamer warship Kasuga and ironclad warship Kōtetsu of the Imperial Japanese Navy

Although the Meiji reformers had overthrown the Tokugawa shogunate, tensions between the former ruler and the restoration leaders led to the Boshin War (January 1868 to June 1869). The early part of the conflict largely involved land battles, with naval forces playing a minimal role transporting troops from western to eastern Japan.[18] Only the Battle of Awa (28 January 1868) was significant; this also proved one of the few Tokugawa successes in the war. Tokugawa Yoshinobu eventually surrendered after the fall of Edo in July 1868, and as a result most of Japan accepted the emperor's rule, however resistance continued in the North.

On 26 March 1868 the first naval review in Japan took place in Osaka Bay, with six ships from the private domain navies of Saga, Chōshū, Satsuma, Kurume, Kumamoto and Hiroshima participating. The total tonnage of these ships was 2,252 tons, which was far smaller than the tonnage of the single foreign vessel (from the French Navy) that also participated. The following year, in July 1869, the Imperial Japanese Navy was formally established, two months after the last combat of the Boshin War.

Enomoto Takeaki, the admiral of the shōgun's navy, refused to surrender all his ships, remitting just four vessels, and escaped to northern Honshū with the remnants of the shōgun's navy: eight steam warships and 2,000 men. Following the defeat of pro-shogunate resistance on Honshū, Admiral Enomoto Takeaki fled to Hokkaidō, where he established the breakaway Republic of Ezo (27 January 1869). The new Meiji government dispatched a military force to defeat the rebels, culminating with the Naval Battle of Hakodate in May 1869.[19] The Imperial side took delivery (February 1869) of the French-built ironclad Kotetsu (originally ordered by the Tokugawa shogunate) and used it decisively towards the end of the conflict.[20]

In February 1868 the Imperial government had placed all captured shogunate naval vessels under the Navy Army affairs section.[18] In the following months, military forces of the government came under the control of several organizations which were established and then disbanded until the establishment of the Ministry of War and of the Ministry of the Navy of Japan in 1872. For the first two years (1868–1870) of the Meiji state no national, centrally controlled navy existed,[21] – the Meiji government only administered those Tokugawa vessels captured in the early phase of the Boshin War of 1868–1869.[21] All other naval vessels remained under the control of the various domains which had been acquired during the Bakumatsu period. The naval forces mirrored the political environment of Japan at the time: the domains retained their political as well as military independence from the Imperial government. Katsu Kaishū a former Tokugawa navy leader, was brought into the government as Vice Minister of the Navy in 1872, and became the first Minister of the Navy from 1873 until 1878 because of his naval experience and his ability to control Tokugawa personnel who retained positions in the government naval forces. Upon assuming office Katsu Kaishu recommended the rapid centralization of all naval forces – government and domain – under one agency.[21] The nascent Meiji government in its first years did not have the necessary political and military force to implement such a policy and so, like much of the government, the naval forces retained a decentralized structure in most of 1869 through 1870.

The incident involving Enomoto Takeaki's refusal to surrender and his escape to Hokkaidō with a large part of the former Tokugawa Navy's best warships embarrassed the Meiji government politically. The imperial side had to rely on considerable naval assistance from the most powerful domains as the government did not have enough naval power to put down the rebellion on its own.[21] Although the rebel forces in Hokkaidō surrendered, the government's response to the rebellion demonstrated the need for a strong centralized naval force.[17] Even before the rebellion the restoration leaders had realized the need for greater political, economic and military centralization and by August 1869 most of the domains had returned their lands and population registers to the government.[17] In 1871 the domains were abolished altogether and as with the political context the centralization of the navy began with the domains donating their forces to the central government.[17] As a result, in 1871 Japan could finally boast a centrally controlled navy, this was also the institutional beginning of the Imperial Japanese Navy.[17]

In February 1872, the Ministry of War was replaced by a separate Army Ministry and Navy Ministry. In October 1873, Katsu Kaishū became Navy Minister.[22]

The ironclad corvette Kongō

In 1870 an Imperial decree determined that Britain's Royal Navy should serve as the model for development, instead of the Netherlands navy.[25] In 1873 a thirty-four-man British naval mission, headed by Lt. Comdr. Archibald Douglas, arrived in Japan. Douglas directed instruction at the Naval Academy at Tsukiji for several years, the mission remained in Japan until 1879, substantially advancing the development of the navy and firmly establishing British traditions within the Japanese navy from matters of seamanship to the style of its uniforms and the attitudes of its officers.[25]

From September 1870, the English Lieutenant Horse, a former gunnery instructor for the Saga fief during the Bakumatsu period, was put in charge of gunnery practice on board the Ryūjō. In 1871, the ministry resolved to send 16 trainees abroad for training in naval sciences (14 to Great Britain, two to the United States), among which was Heihachirō Tōgō. Later, Commander L.P. Willan was hired in 1879 to train naval cadets.[25]

Ships such as the Fusō, Kongō and Hiei were built in British shipyards, and they were the first warships built abroad specifically for the Imperial Japanese Navy.[23][26] Private construction companies such as Ishikawajima and Kawasaki also emerged around this time.

During 1873, a plan to invade the Korean Peninsula, the Seikanron proposal made by Saigō Takamori, was narrowly abandoned by decision of the central government in Tokyo.[27] In 1874, the Taiwan expedition was the first foray abroad of the new Imperial Japanese Navy and Army after the Mudan Incident of 1871, however the navy served largely as a transport force.[24]

Various interventions in the Korean Peninsula continued in 1875–1876, starting with the Ganghwa Island incident provoked by the Japanese gunboat Un'yō, leading to the dispatch of a large force of the Imperial Japanese Navy. As a result, the Japan–Korea Treaty of 1876 was signed, marking the official opening of Korea to foreign trade, and Japan's first example of Western-style interventionism and adoption of "unequal treaties" tactics.[28]

In 1878, the Japanese cruiser Seiki sailed to Europe with an entirely Japanese crew.

After the Imo Incident in July 1882, Iwakura Tomomi submitted a document to the daijō-kan titled "Opinions Regarding Naval Expansion" asserting that a strong navy was essential to maintaining the security of Japan.[29] In furthering his argument, Iwakura suggested that domestic rebellions were no longer Japan's primary military concern and that naval affairs should take precedence over army concerns; a strong navy was more important than a sizable army to preserve the Japanese state.[29] Furthermore, he justified that a large, modern navy, would have the added potential benefit of instilling Japan with greater international prestige[29] and recognition, as navies were internationally recognized hallmarks of power and status.[30] Iwakura also suggested that the Meiji government could support naval growth by increasing taxes on tobacco, sake, and soy.[30]

After lengthy discussions, Iwakura eventually convinced the ruling coalition to support Japan's first multi-year naval expansion plan in history.[30] In May 1883, the government approved a plan that, when completed, would add 32 warships over eight years at a cost of just over ¥26 million.[30] This development was very significant for the navy, as the amount allocated virtually equaled the navy's entire budget between 1873 and 1882.[30] The 1882 naval expansion plan succeeded in a large part because of Satsuma power, influence, and patronage.[31] Between 19 August and 23 November 1882, Satsuma forces with Iwakura's leadership, worked tirelessly to secure support for the Navy's expansion plan.[31] After uniting the other Satsuma members of the Dajokan, Iwakura approached the emperor the Meiji emperor arguing persuasively just as he did with the Dajokan, that naval expansion was critical to Japan's security and that the standing army of forty thousand men was more than sufficient for domestic purposes.[31] While the government should direct the lion's share of future military appropriations toward naval matters, a powerful navy would legitimize an increase in tax revenue.[32] On November 24, the emperor assembled select ministers of the daijō-kan together with military officers, and announced the need for increased tax revenues to provide adequate funding for military expansion, this was followed by an imperial re-script. The following month, in December, an annual ¥7.5-million tax increase on sake, soy, and tobacco was fully approved, in the hopes that it would provide ¥3.5 million annually for warship construction and ¥2.5 million for warship maintenance.[32] In February 1883, the government directed further revenues from other ministries to support an increase in the navy's warship construction and purchasing budget. By March 1883, the navy secured the ¥6.5 million required annually to support an eight-year expansion plan, this was the largest that the Imperial Japanese Navy had secured in its young existence.[32]

However, naval expansion remained a highly contentious issue for both the government and the navy throughout much of the 1880s. Overseas advances in naval technology increased the costs of purchasing large components of a modern fleet, so that by 1885 cost overruns had jeopardized the entire 1883 plan. Furthermore, increased costs coupled with decreased domestic tax revenues, heightened concern and political tension in Japan regarding funding naval expansion.[30] In 1883, two large warships were ordered from British shipyards.

The Naniwa and Takachiho were 3,650 ton ships. They were capable of speeds up to 18 kn (33 km/h; 21 mph) and were armed with 54 to 76 mm (2 to 3 in) deck armor and two 260 mm (10 in) Krupp guns. The naval architect Sasō Sachū designed these on the line of the Elswick class of protected cruisers but with superior specifications.[33] An arms race was taking place with China however, who equipped herself with two 7,335 ton German-built battleships (Ting Yüan and Chen-Yüan). Unable to confront the Chinese fleet with only two modern cruisers, Japan resorted to French assistance to build a large, modern fleet which could prevail in the upcoming conflict.[33]

The French-built protected cruiser Matsushima, the flagship of the IJN at the Battle of the Yalu River in 1894

The protected cruiser Hashidate, built domestically at the arsenal of Yokosuka

During the 1880s, France took the lead in influence, due to its "Jeune École" ("young school") doctrine, favoring small, fast warships, especially cruisers and torpedo boats, against bigger units.[33] The choice of France may also have been influenced by the Minister of the Navy, who happened to be Enomoto Takeaki at that time (Navy Minister 1880–1885), a former ally of the French during the Boshin War. Also, Japan was uneasy with being dependent on Great Britain, at a time when Great Britain was very close to China.[34]

The Meiji government issued its First Naval Expansion bill in 1882, requiring the construction of 48 warships, of which 22 were to be torpedo boats.[33] The naval successes of the French Navy against China in the Sino-French War of 1883–85 seemed to validate the potential of torpedo boats, an approach which was also attractive to the limited resources of Japan.[33] In 1885, the new Navy slogan became Kaikoku Nippon (Jp:海国日本, "Maritime Japan").[35]

In 1885, the leading French Navy engineer Émile Bertin was hired for four years to reinforce the Japanese Navy and to direct the construction of the arsenals of Kure and Sasebo.[33] He developed the Sankeikan class of cruisers; three units featuring a single powerful main gun, the 320 mm (13 in) Canet gun.[33] Altogether, Bertin supervised the building of more than 20 units. They helped establish the first true modern naval force of Japan. It allowed Japan to achieve mastery in the building of large units, since some of the ships were imported, and some others were built domestically at the arsenal of Yokosuka:

• 3 cruisers: the 4,700 ton Matsushima and Itsukushima, built in France, and the Hashidate, built at Yokosuka.[34]
• 3 coastal warships of 4,278 tons.
• 2 small cruisers: the Chiyoda, a small cruiser of 2,439 tons built in Britain, and the Yaeyama, 1,800 tons, built at Yokosuka.
• 1 frigate, the 1,600 ton Takao, built at Yokosuka.[36]
• 1 aviso: the 726 ton Chishima, built in France.
• 16 torpedo boats of 54 tons each, built in France by the Companie du Creusot in 1888, and assembled in Japan.[34]

This period also allowed Japan "to embrace the revolutionary new technologies embodied in torpedoes, torpedo-boats and mines, of which the French at the time were probably the world's best exponents".[37] Japan acquired its first torpedoes in 1884, and established a "Torpedo Training Center" at Yokosuka in 1886.[33]

These ships, ordered during the fiscal years 1885 and 1886, were the last major orders placed with France. The unexplained sinking of Unebi en route from France to Japan in December 1886, created embarrassment however.[34][38]

The torpedo boat Hayabusa

Japan turned again to Britain, with the order of a revolutionary torpedo boat, Kotaka, which was considered the first effective design of a destroyer,[33] in 1887 and with the purchase of Yoshino, built at the Armstrong works in Elswick, Newcastle upon Tyne, the fastest cruiser in the world at the time of her launch in 1892.[33] In 1889, she ordered the Clyde-built Chiyoda, which defined the type for armored cruisers.[39]

Between 1882 and 1918, ending with the visit of the French Military Mission to Japan, the Imperial Japanese Navy stopped relying on foreign instructors altogether. In 1886, she manufactured her own prismatic powder, and in 1892 one of her officers invented a powerful explosive, the Shimose powder.

In the years following after the end of First World War the naval construction programs of the three greatest naval powers Britain, Japan and the United States had threatened to set off a new potentially dangerous and expensive naval arms race.[79] The subsequent Washington Naval Treaty of 1922 became one of history's most effective arms reduction programs,[80] setting up a system of ratios between the five signatory powers. The United States and Britain were each allocated 525,000 tons of capital ships, Japan 315,000, and France and Italy to 175,000, ratios of 5:3:1.75.[81] Also agreed to was a ten-year moratorium on battleship construction, though replacement of battleships reaching 20 years of service was permitted. Maximum limits of 35,000 tons and 16-inch guns were also set. Carriers were restricted with the same 5:5:3 ratio, with Japan allotted 81,000 tons.[81]

Many naval leaders in Japan's delegation were outraged by these limitations, as Japan would always be behind its chief rivals. However, in the end it was concluded that even these unfavorable limitations would be better than an unrestricted arms race with the industrially dominant United States.[82] The Washington System may have made Japan a junior partner with the US and Britain, but it also curtailed the rise of China and the Soviet Union, who both sought to challenge Japan in Asia.[83]

The Washington Treaty did not restrict the building of ships other than battleships and carriers, resulting in a building race for heavy cruisers. These were limited to 10,000 tons and 8-inch guns.[84] The Japanese were also able to get some concessions, most notably the battleship Mutsu,[85] which had been partly funded by donations from schoolchildren and would have been scrapped under the terms of the treaty.

The Treaty also dictated that the United States, Britain, and Japan could not expand their Western Pacific fortifications. Japan specifically could not militarize the Kurile Islands, the Bonin Islands, Amami-Oshima, the Loochoo Islands, Formosa and the Pescadores.[86]

Captain Sempill showing a Sparrowhawk fighter to Admiral Tōgō Heihachirō, 1921

Japan at times continued to solicit foreign expertise in areas in which the IJN was inexperienced, such as naval aviation. The Japanese navy had closely monitored the progress of aviation of the three Allied naval powers during World War I and concluded that Britain had made the greatest advances in naval aviation,.[87] The Sempill Mission led by Captain William Forbes-Sempill, a former officer in the Royal Air Force experienced in the design and testing of Royal Navy aircraft during the First World War.[88] The mission consisted of 27 members, who were largely personnel with experience in naval aviation and included pilots and engineers from several British aircraft manufacturing firms.[88] The British technical mission left for Japan in September with the objective of helping the Imperial Japanese Navy develop and improve the proficiency of its naval air arm.[88] The mission arrived at Kasumigaura Naval Air Station the following month, in November 1921, and stayed in Japan for 18 months.[89]

The mission brought to Kasumigaura well over a hundred British aircraft comprising twenty different models, five of which were then currently in service with the Royal Navy's Fleet Air Arm. The Japanese were trained on several, such as the Gloster Sparrowhawk, then a frontline fighter. The Japanese would go on to order 50 of these aircraft from Gloster, and build 40.[90] These planes eventually provided the inspiration for the design of a number of Japanese naval aircraft. Technicians become familiar with the newest aerial weapons and equipment-torpedoes, bombs, machine guns, cameras, and communications gear.[88] Japanese naval aviators were trained in various techniques such as torpedo bombing, flight control and carrier landing and take-offs.

The mission also brought the plans of the most recent British aircraft carriers, such as HMS Argus and HMS Hermes, which influenced the final stages of the development of the carrier Hōshō. By the time its last members had returned to Britain, the Japanese had acquired a reasonable grasp of the latest aviation technology and taken the first steps toward having an effective naval air force.[91] Japanese naval aviation also, both in technology and in doctrine, continued to be dependent on the British model for most of the 1920s.[92]

Hōshō, the world's first purpose built aircraft carrier, completed in 1922

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

• In 1921, it launched 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 Japanese Navy was the first to mount 356 mm (14 in) guns (in Kongō), 410 mm (16.1 in) guns (in Nagato), and began the only battleships ever to mount 460 mm (18.1 in) guns (in the Yamato class).[93]
• 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.[94]
• Japan developed the 610 mm (24 in) oxygen fuelled Type 93 torpedo, generally recognized as the best torpedo of World War II.[95]

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.[96] 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 assault. 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.

This was in conflict with Japan's doctrine of "decisive battle" (艦隊決戦, Kantai kessen, which did not require long range),[97] in which IJN would allow the US to sail across the Pacific, using submarines to damage it, then engage the US Navy in a "decisive battle area" near Japan after inflicting such attrition.[98] This is also 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,[99] as they had been for over 300 years.

Following the dictates of Satō (who doubtless was influenced by Mahan),[100] 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 US' insistence on a 60% ratio, which meant parity.[101] 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), but failed to take account of any of these traits. Her opponents in any future Pacific War would not face the political and geographical constraints of her previous wars, nor did she allow for losses in ships and crews.[102]

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 aircraft carriers. Neither really prevailed, and both types were developed. The result was that neither ended up with overwhelming strength over its American adversary.

A consistent weakness of gunned Japanese warship development was the tendency to incorporate too much armament, and too much engine power, relative to ship size (a side-effect of the Washington Treaty limitations on overall tonnage), leading to shortcomings in stability, protection and structural strength.[103]

The battleships Yamashiro and Fusō and the battlecruiser Haruna, Tokyo Bay, 1930s

In response to the London Treaty of 1930, the Japanese started a series of naval construction programs or hoju keikaku (naval replenishment, or construction, plans), known unofficially as the maru keikaku (circle plans). Between 1930 and the outbreak of the Second World War there were four of these "Circle plans" which were drawn up in 1931, 1934, 1937, and 1939.[104] The Circle One was plan approved in 1931, provided for the construction of 39 ships to be laid down between 1931 and 1934, centering on four of the new Mogami-class cruisers,[105] and expansion of the Naval Air Service to 14 Air Groups. However, plans for a second Circle plan were delayed by the Tomozuru capsizing and heavy typhoon damage to the Fourth fleet, when it was revealed that the basic designs of many Japanese warships were flawed due to poor construction techniques and instability caused by attempting to mount too much weaponry on too small a displacement hull.[106] As a result, most of the naval budget in 1932–1933 was absorbed in modifications to rectify the issues with existing equipment.[106]

In 1934, the Circle Two plan was approved, covering the construction of 48 new warships including the Tone-class cruisers and two carriers: Sōryū and Hiryū. The plan also continued the buildup in naval aircraft and authorized the creation of eight new Naval Air Groups. With Japan's renunciation of naval treaties in December 1934, Circle Three plan was approved in 1937, its third major naval building program since 1930.[107] A six-year effort, it called for construction of new warships that were free from the old treaty restrictions, while concentrating on qualitative superiority to compensate for Japan's quantitative deficiencies compared with the United States. While the core of Circle three was to be the construction of the two battleships Yamato and Musashi, it also called for building the two Shōkaku-class aircraft carrier, along with sixty-four other warships in other categories.[107] Circle Three also called for the rearming of the demilitarized battlecruiser Hiei and the refitting of her sister ships, Kongō, Haruna, and Kirishima.[107] Also funded was upgrading of the four Mogami-class cruisers and the two Tone class cruisers, which were under construction, by replacing their 6-inch main batteries with 8-inch guns.[107] In aviation, Circle Three aimed at maintaining parity with American naval air power by adding 827 planes for allocation to fourteen planned land-based air groups, and increasing carrier aircraft by nearly 1,000. To accommodate the new land aircraft the plan called for several new airfields to be built or expanded; it also provided for a significant increase in the size of the navy's production facilities for aircraft and aerial weapons.[107]

In 1938, with the construction of Circle Three under way, the Japanese had begun to consider preparations for the next major expansion, which was scheduled for 1940. However, with the American second Vinson act in 1938, the Japanese accelerated the Circle Four six-year expansion program, which was approved in September 1939.[108] Circle Four's goal was doubling Japan's naval air strength in just five years, delivering air superiority in East Asia and the western Pacific.[108] It called for building of two Yamato-class battleship, a fleet carrier, six of a new class of planned escort carriers, six cruisers, twenty-two destroyers, and twenty-five submarines. The real emphasis, however, was on naval air power, in which the Japanese hoped to take the lead.

To achieve Asian air superiority Circle Four planned for the acquisition of 175 ship based aircraft and nearly 1,500 land based aircraft to be allocated to seventy-five new air groups. Upon completion of this expansion Japan would have 874 ship-based aircraft and 3,341 aircraft in 128 land based air groups, 65 of these being combat air groups and 63 training.

Type 91 Aerial Torpedo aboard the aircraft carrier Akagi

The China War was of great importance and value to the development of Japanese naval aviation, demonstrating how aircraft could contribute to the projection of naval power ashore.[109]

The IJN had two primary responsibilities during it: to support amphibious operations on the Chinese coast and the strategic aerial bombardment of Chinese cities[110] – the first time any naval air arm had been given such tasks.[110]

From the onset of hostilities in 1937 until forces were diverted to combat for the Pacific war in 1941, naval aircraft played a key role in military operations on the Chinese mainland. These began with attacks on military installations largely in the Yangtze River basin along the Chinese coast by Japanese carrier aircraft.[110] Naval involvement during the conflict peaked in 1938–39 with the heavy bombardment of Chinese cities deep in the interior by land-based medium bombers and concluded during 1941 with an attempt by both, carrier-borne and land-based, tactical aircraft to cut communication and transportation routes in southern China. Although, the 1937–41 air offensives failed in their political and psychological aims, they did reduce the flow of strategic materiel to China and for a time improved the Japanese military situation in the central and southern parts of the country.[110]

Following Japan's surrender and subsequent occupation by the Allies at the conclusion of World War II, the Imperial Japanese Navy, along with the rest of the Japanese military, was dissolved in 1945. In the new constitution of Japan which was drawn up in 1947, Article 9 specifies that "The Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as a means of settling international disputes."[130] The prevalent view in Japan is that this article allows for military forces to be kept for the purposes of self-defense.[131]

In 1952, the Coastal Safety Force was formed within the Maritime Safety Agency, incorporating the minesweeping fleet and other military vessels, mainly destroyers, given by the United States. In 1954, the Coastal Safety Force was separated, and the JMSDF was formally created as the naval branch of the Japanese Self-Defense Force (JSDF), following the passage of the 1954 Self-Defense Forces Law. Japan's current navy falls under the umbrella of the Japan Self-Defense Forces (JSDF) as the Japan Maritime Self-Defense Force (JMSDF).[132][133][134][135][136][137][138]