The origins of the Imperial Japanese Navy trace back to early interactions with nations on the Asian continent, beginning in the early medieval period and reaching a peak of activity during the 16th and 17th centuries at a time of cultural exchange with European powers during the Age of Discovery. After two centuries of stagnation during the country's ensuing seclusion policy under the shoguns of the Edo period, Japan's navy was comparatively backward when the country was forced open to trade by American intervention in 1854. This eventually led to the Meiji Restoration. Accompanying the re-ascendance of the Emperor came a period of frantic modernization and industrialization. The navy's history of successes, sometimes against much more powerful foes as in the Sino-Japanese war and the Russo-Japanese War, ended in almost complete annihilation during the concluding days of World War II. The IJN was officially dissolved in 1947.
Japan has a long history of naval interaction with the Asian continent, involving transportation of troops between Korea and Japan, starting at least with the beginning of the Kofun period in the 3rd century.
Japan undertook major naval building efforts in the 16th century, during the Warring States period, when feudal rulers vying for supremacy built vast coastal navies of several hundred ships. Around that time, Japan may have developed one of the first ironclad warships, when Oda Nobunaga, a Japanese daimyo, had six iron-covered Oatakebune made in 1576. In 1588, Toyotomi Hideyoshi issued a ban on Wakō piracy; the pirates then became vassals of Hideyoshi, and comprised the naval force used in the Japanese invasion of Korea.
Japan built her first large ocean-going warships in the beginning of the 17th century, following contacts with the Western nations during the Nanban trade period. In 1613, the Daimyo of Sendai, in agreement with the Tokugawa Bakufu, built Date Maru, a 500 ton galleon-type ship that transported the Japanese embassy of Hasekura Tsunenaga to the Americas, which then continued to Europe. From 1604, about 350 Red seal ships, usually armed and incorporating some Western technologies, were also commissioned by the Bakufu, mainly for Southeast Asian trade.
Beginning in 1640, for more than 200 years Japan chose "sakoku" (seclusion), which forbade contacts with the West, eradicated Christianity, and prohibited the construction of ocean-going ships on pain of death. Contacts were maintained through the Dutch enclave of Dejima however, allowing for the transfer of a vast amount of knowledge related to the Western technological and scientific revolution. This study of Western sciences, called "rangaku", also allowed Japan to remain updated in areas relevant to naval sciences, such as cartography, optics or mechanical sciences. The full study of Western shipbuilding techniques resumed in the 1840s during the Late Tokugawa shogunate (Bakumatsu).
As soon as Japan agreed to open up to foreign influence, the Tokugawa shogun government initiated an active policy of assimilation of Western naval technologies. In 1855, with Dutch assistance, the Shogunate acquired its first steam warship, Kankō Maru, which was used for training, and established the Nagasaki Naval Training Center. In 1857, it acquired its first screw-driven steam warship, the Kanrin Maru. In 1859, the Naval Training Center was transferred to Tsukiji in Tokyo. Naval students were sent to study in Western naval schools for several years, such as the future Admiral Takeaki Enomoto (who studied in the Netherlands from 1862–1867), starting a tradition of foreign-educated future leaders such as Admirals Heihachiro Togo and, later, Isoroku Yamamoto.
As early as 1863, less than 10 years after opening the country to foreign interaction, Japan completed her first domestically-built steam warship, Chiyodagata. In 1865, the French naval engineer Léonce Verny was hired to build Japan's first modern naval arsenals, at Yokosuka and Nagasaki. In 1867–1868, a British Naval mission headed by Captain Tracey was sent to Japan to assist the development of the Navy and organize the naval school of Tsukiji.
By the end of the Tokugawa shogunate in 1867, the Tokugawa navy was already the largest of Eastern Asia, organized around eight Western-style steam warships and the flagship Kaiyō Maru, which were used against pro-imperial forces during the Boshin War, under the command of Admiral Enomoto. The conflict culminated with the Naval Battle of Hakodate in 1869, Japan's first large-scale modern naval battle, and ended with the defeat of the last Tokugawa forces and the restoration of Imperial rule. The revolutionary French-built ironclad Kotetsu, originally ordered by the Tokugawa shogunate, was received by the Imperial side and was used decisively towards the end of the conflict.
From 1868, the restored Meiji Emperor continued with reforms to industrialize and militarize Japan to prevent the United States and European powers from overwhelming her. On 17 January 1868, the Ministry of Military Affairs (兵部省, also known as the Army-Navy Ministry) was established, with Iwakura Tomomi, Shimazu Tadayoshi and Prince Komatsu-no-miya Akihito as the First Secretaries.
On 26 March 1868, the first Naval Review was held in Japan (in Osaka Bay), with 6 ships from the private domainal navies of Saga, Chōshū, Satsuma, Kurume, Kumamoto and Hiroshima participating. The total tonnage of these ships was 2252 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.
In July 1869, the private domanial navies were abolished, and their 11 ships were added to the 7 surviving vessels of the defunct Tokugawa bakufu navy to form the core of the new Imperial Japanese Navy. In February 1872, the Ministry of Military Affairs was replaced by a separate Army Ministry (陸軍省) and Navy Ministry (海軍省). In October 1873, Katsu Kaishu became Navy Minister. The new government drafted an ambitious plan to create a Navy with 200 ships organized into 10 fleets. It was abandoned within a year due to lack of resources.
During the 1870s and 1880s, the Imperial Japanese Navy remained an essentially coastal defense force, although the Meiji government continued to modernize it. Jho Sho Maru (soon renamed Ryūjō Maru) commissioned by Thomas Glover was launched at Aberdeen, Scotland on 27 March 1869. In 1870, an Imperial decree determined that Britain's Royal Navy should be the model for development, instead of the Netherlands.
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 onboard the Ryūjō. In 1871, the Ministry resolved to send 16 trainees abroad for training in naval sciences (14 to Great Britain, 2 to the United States), among which was Togo Heihachiro. A 34-member British naval mission visited Japan in 1873 for two years, headed by Comdr. Archibald Douglas. Later, Comdr. L.P. Willan was hired in 1879 to train naval cadets.
During 1873, a plan to invade the Korean peninsula (the Seikanron proposal made by Saigo Takamori) was narrowly abandoned by decision of the central government in Tokyo. In 1874, the Taiwan expedition was the first foray abroad of the new Imperial Japanese Navy and the Imperial Japanese Army.
Various interventions in the Korean peninsula continued in 1875–1876, starting with the Ganghwa Island incident (江華島事件) provoked by the Japanese gunboat Unyo, leading to the dispatch of a large force of the Imperial Japanese Navy. As a result, the Treaty of Ganghwa 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.
Soon, however domestic rebellions, the Saga Rebellion (1874) and especially the Satsuma Rebellion (1877), forced the government to focus on land warfare. Naval policy, expressed by the slogan Shusei Kokubō (Jp:守勢国防, lit. "Static Defense"), focused on coastal defenses and a standing army (established with the assistance of the second French Military Mission to Japan), and a coastal Navy, leading to a military organization under the Rikushu Kaijū (Jp:陸主海従, Army first, Navy second) principle.
In 1878, the Japanese cruiser Seiki sailed to Europe with an entirely Japanese crew.
In 1883 two large warships were ordered from British shipyards. Naniwa and the Takachiho were 3,650-ton ships. They were capable of speeds up to 18 knots (33 km/h) and were armed with 2 to 3-inch deck armor and two 10.2-in (260 mm) Krupp guns. The naval architect Sasō Sachū designed these on the line of the Elswick class of protected cruisers but with superior specifications. An arms race was taking place with China however, who equipped herself with two German-built battleships of 7,335 tons (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.
During the 1880s, France took the lead in influence, due to its "Jeune Ecole" ("young school") doctrine, favoring small, fast warships, especially cruisers and torpedo boats, against bigger units. The choice of France may also have been influenced by the Minister of the Japanese Navy (海軍卿), who happened to be Enomoto Takeaki at that time (Navy Minister 1880–1885), a former ally of the French during the Boshin War.
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. 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. In 1885, the new Navy slogan became Kaikoku Nippon (Jp:海国日本, lit. "Maritime Japan").
In 1885, the leading French Navy engineer Emile Bertin was hired for four years to reinforce the Japanese Navy and to direct the construction of the arsenals of Kure and Sasebo. He developed the Sanseikan class of cruisers; 3 units featuring a single powerful main gun, the 12.6in (320 mm) Canet gun. Altogether, Bertin supervised the building of more than twenty 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:
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". Japan acquired its first torpedoes in 1884, and established a "Torpedo Training Center" at Yokosuka in 1886.
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 diplomatic frictions and doubts about the French designs.
Japan turned again to Britain, with the order of a revolutionary torpedo boat, Kotaka (considered the first ever effective design of a destroyer), 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. In 1889, she ordered the Clyde-built Chiyoda'', which defined the type for armored cruisers.
After 1882 (until 1918, 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.
Japan continued the modernization of its navy, especially as China was also building a powerful modern fleet with foreign, especially German, assistance, and the pressure was building between the two countries to take control of Korea. The Sino-Japanese war was officially declared on 1 August 1894, though some naval fighting had already taken place.
The Japanese navy devastated Qing's Beiyang Fleet off the mouth of the Yalu River at the Battle of Yalu River on 17 September 1894, in which the Chinese fleet lost 8 out of 12 warships. Although Japan turned out victorious, the two large German-made battleships of the Chinese Navy remained almost impervious to Japanese guns, highlighting the need for bigger capital ships in the Japanese Navy (Ting Yuan was finally sunk by torpedoes, and Chen-Yuan was captured with little damage). The next step of the Imperial Japanese Navy's expansion would thus involve a combination of heavily armed large warships, with smaller and innovative offensive units permitting aggressive tactics.
As a result of the conflict, under the Treaty of Shimonoseki (April 17th, 1895), Taiwan and the Pescadores Islands were transferred to Japan. The Imperial Japanese Navy took possession of the island and quelled opposition movements between March to October 1895, and the islands continued to be a Japanese colony until 1945. Japan also obtained the Liaodong Peninsula, although she was forced by Russia to return it to China, only to see Russia take possession of it soon after.
The Imperial Japanese Navy further intervened in China in 1900, by participating together with Western Powers to the suppression of the Chinese Boxer Rebellion. The Navy supplied the largest number of warships (18 out of a total of 50) and delivered the largest contingent of troops among the intervening nations (20,840 Imperial Japanese Army and Navy soldiers, out of total of 54,000).
The conflict allowed Japan to combat together with Western nations, and to acquire first hand understanding of their fighting methods.
Following the Sino-Japanese War, and the humiliation of the forced return of the Liaotung peninsula to China under Russian pressure (the "Triple Intervention"), Japan began to build up its military strength in preparation for further confrontations. Japan promulgated a ten-year naval build-up program, under the slogan "Perseverance and determination" (臥薪嘗胆, Gashinshōtan), in which it commissioned 109 warships, for a total of 200,000 tons, and increased its Navy personnel from 15,100 to 40,800. The new fleet consisted of:
One of these battleships, Mikasa, the most advanced ship of her time, was ordered from the Vickers shipyard in the United Kingdom at the end of 1898, for delivery to Japan in 1902. Commercial shipbuilding in Japan was exhibited by construction of the twin screw steamer Aki-Maru, built for Nippon Yusen Kaisha by the Mitsubishi Dockyard & Engine Works, Nagasaki. The Imperial Japanese cruiser Chitose was built at the Union Iron Works in San Francisco, California.
These dispositions culminated with the Russo-Japanese War. At the Battle of Tsushima, Admiral Togo (flag in Mikasa) led the Japanese Combined Fleet into the decisive engagement of the war. The Russian fleet was almost completely annihilated: out of 38 Russian ships, 21 were sunk, 7 captured, 6 disarmed, 4,545 Russian servicemen died and 6,106 were taken prisoner. On the other hand, the Japanese only lost 116 men and 3 torpedo boats. These victories broke Russian strength in East Asia, and triggered waves of mutinies in the Russian Navy at Sevastopol, Vladivostok and Kronstadt, peaking in June with the Potemkin rising, thereby contributing to the Russian Revolution of 1905.
During the Russo-Japanese war, Japan also made frantic efforts to develop and construct a fleet of submarines. Submarines had only recently become operational military engines, and were considered to be special weapons of considerable potential.
The Imperial Japanese Navy acquired its first submarines in 1905 from Electric Boat Company, barely four years after the U.S. Navy had commissioned its own first submarine, USS Holland. The ships were Holland designs and were developed at the Fore River Ship and Engine Company under the supervision of Electric Boat's representative, Arthur L. Busch. These five submarines (known as Holland Type VII's) were shipped in kit form by freighter to Japan (October 1904) and then assembled under Busch's supervision at the Yokosuka, Kanagawa Yokosuka Naval Arsenal, to become hulls No1 through 5, and became operational at the end of 1905.
Japan continued in its efforts to build up a strong national naval industry. Following a strategy of "Copy, improve, innovate", foreign ships of various designs were usually analysed in depth, their specifications often improved on, and then were purchased in pairs so as to organize comparative testing and improvements. Over the years, the importation of whole classes of ships was progressively substituted by local assembly, and then complete local production, starting with the smallest ships, such as torpedo boats and cruisers in the 1880s, to finish with whole battleships in the early 1900s. The last major purchase was in 1913 when the battlecruiser Kongō was purchased from the Vickers shipyard. By 1918, there was no aspect of shipbuilding technology where Japanese capabilities fell significantly below world standards.
The period immediately after Tsushima also saw the IJN, under the influence of the navalist theoretician Satō Tetsutarō, adopt an explicit policy of building for a potential future conflict against the United States Navy. Satō called for a battlefleet at least 70% as strong as that of the USA. In 1907, the official policy of the Navy became an 'eight-eight fleet' of eight modern battleships and eight battlecruisers. However, financial constraints prevented this ideal ever becoming a reality.
By 1920, the Imperial Japanese Navy was the world's third largest navy, and was a leader in many aspects of naval development:
In the Battle of Tsingtao, the Japanese Navy seized the German naval base of Tsingtao. During the battle, beginning on 5 September 1914, Wakamiya conducted the world's first sea-launched air strikes. from Kiaochow Bay. Four Maurice Farman seaplanes bombarded German land targets (communication centers and command centers) and damaged a German minelayer in the Tsingtao peninsula from September to 6 November 1914 when the Germans surrendered.
Concurrently, a battle group was sent to the central Pacific in August and September to pursue the German East Asiatic squadron, which then moved into the Southern Atlantic, where it encountered British naval forces and was destroyed at the Battle of the Falkland Islands. Japan seized former German possessions in Micronesia (the Mariana Islands, excluding Guam); the Caroline Islands; and the Marshall Islands), which remained Japanese colonies until the end of World War II, under the League of Nations' South Pacific Mandate.
Hard pressed in Europe, where she had only a narrow margin of superiority against Germany, Britain had requested, but was denied, the loan of Japan's four newest Kongō-class battleships (Kongō, Hiei, Haruna, and Kirishima), the first ships in the world to be equipped with 14-inch (356 mm) guns, and the most formidable capital ships in the world at the time. The British 15-inch-gunned battleships would come into use during the war.
Following a further request to contribute to the conflict, and the advent of unrestricted submarine warfare by Germany, the Imperial Navy in March 1917 sent a special force of destroyers to the Mediterranean. This force, consisting of one armoured cruiser, Akashi, as flotilla leader, and eight of the Navy's newest destroyers (Ume, Kusunoki, Kaede, Katsura, Kashiwa, Matsu, Sugi, and Sakaki), under Admiral Satō Kōzō, was based in Malta and efficiently protected allied shipping between Marseille, Taranto, and ports in Egypt until the end of the War. In June, Akashi was replaced by Izumo, and four more destroyers were added (Kashi, Hinoki, Momo, and Yanagi). They were later joined by the cruiser Nisshin. By the end of the war, the Japanese had escorted 788 allied transports. One destroyer, Sakaki, was torpedoed by an Austrian submarine with the loss of 59 officers and men.
In 1918, ships such as Azuma were assigned to convoy escort in the Indian Ocean between Singapore and the Suez Canal as part of Japan’s contribution to the war effort under the Anglo-Japanese alliance.
After the conflict, the Japanese Navy received seven German submarines as spoils of war, which were brought to Japan and analysed, contributing greatly to the development of the Japanese submarine industry.
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.'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.
During the interwar, Japan took the lead in many areas of warship development:
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. This was a failing of Japanese naval architects, reflecting her industrial and engineering weakness.
The Imperial Japanese Navy of World War II was administered by the Ministry of the Navy of Japan and controlled by the Chief of the Imperial Japanese Navy General Staff at Imperial General Headquarters. In order to combat the numerically superior American navy, the IJN devoted large amounts of resources to creating a force superior in quality to any navy at the time. Consequently, at the beginning of World War II, Japan probably had the most sophisticated Navy in the world. Betting on the speedy success of aggressive tactics (stemming from Mahanian doctrine and the lure of "decisive battle"), Japan did not invest significantly on defensive organization: she needed to protect her long shipping lines against enemy submarines, which she never managed to do, particularly under-investing in the vital role of antisubmarine warfare (both escort ships and escort aircraft carriers), and in the specialized training and organization to support it.
IJN enjoyed spectacular success during the first part of the hostilities, but American forces ultimately managed to gain the upper hand through technological upgrades to its air and naval forces and a vastly greater industrial output. Japan's reluctance to use their submarine fleet for commerce raiding and failure to secure their communications also hastened her defeat. During the last phase of the war, the Imperial Japanese Navy resorted to a series of desperate measures, including a variety of Special Attack Units (popularly called kamikaze).
Japan continued to attribute considerable prestige to battleships and endeavoured to build the largest and most powerful ships of the period. Yamato, the largest and most heavily-armed battleship in history, was launched in 1941.
The second half of World War II saw the last battleship duels. In the Battle of Guadalcanal on 15 November 1942, the United States battleships South Dakota and Washington fought and destroyed the Japanese battleship Kirishima. In the Battle of Leyte Gulf on 25 October 1944 six battleships, led by Admiral Jesse Oldendorf of the U.S. 7th Fleet fired upon and claimed credit for sinking Admiral Shoji Nishimura's battleships Yamashiro and Fusō during the Battle of Surigao Strait; in fact, both battleships were fatally crippled by destroyer attacks before being brought under fire by Oldendorf's old battleships.
Nevertheless, the Battle off Samar on 25 October 1944 during the Battle of Leyte Gulf showed battleships could still be useful. Only the indecision of Admiral Takeo Kurita and the fight by American destroyers and destroyer escorts saved the American aircraft carriers of "Taffy 3" from destruction by the gunfire of Yamato, Kongō, Haruna, and Nagato and their cruiser escort. Miraculously for the Americans, only USS Gambier Bay, along with two destroyers and one destroyer escort, were lost in this action.
Ultimately, the maturity of air power spelled doom for the battleship. Battleships in the Pacific ended up primarily performing shore bombardment and anti-aircraft defense for the carriers. Yamato and Musashi were sunk by air attacks long before coming in gun range of the American fleet. As a result of the changing technology, plans for even larger battleships, such as the Japanese Super Yamato class, were cancelled.
From 1935-1938, Akagi and Kaga received extensive rebuilds to improve their aircraft handling capacity. Japan put particular emphasis on aircraft carriers. The Imperial Japanese Navy started the Pacific War with 10 aircraft carriers, the largest and most modern carrier fleet in the world at that time. There were seven American aircraft carriers at the beginning of hostilities, only three operating in the Pacific; and eight British aircraft carriers, of which a single one operated in the Indian Ocean. The IJN's two Shōkaku-class carriers were superior to any carrier in the world, until the wartime appearance of the American Essex-class. A large number of these Japanese carriers were of small size, however, in accordance with the limitations placed upon the Navy by the London and Washington Naval Conferences.
Following the Battle of Midway, in which four Japanese fleet carriers were sunk, the Japanese Navy suddenly found itself short of fleet carriers (as well as trained aircrews), resulting in an ambitious set of projects to convert commercial and military vessels into escort carriers, such as the Hiyō. Another conversion project, Shinano, was based on an incomplete Yamato-class super battleship and became the largest-displacement carrier of World War II. The IJN also attempted to build a number of fleet carriers, though most of these projects were not completed by the end of the war. One exception being the Taihō, which was the first and only Japanese carrier with an armored flight deck and first to incorporate a closed hurricane bow.
Japan began the war with a highly competent naval air force designed around some of the best airplanes in the world: the Zero was considered the best carrier aircraft of the beginning of the war, the Mitsubishi G3M bomber was remarkable for its range and speed, and the Kawanishi H8K was world's best flying boat. The Japanese pilot corps at the beginning of the war were of high caliber as compared to their contemporaries around the world due to intense training and frontline experience in the Sino-Japanese War. The Navy also had a competent tactical bombing force based around the Mitsubishi G3M and G4M bombers, which astonished the world by being the first planes to sink enemy capital ships underway, claiming battleship Prince of Wales and the battlecruiser Repulse.
As the war dragged on, the Allies found weaknesses in Japanese Naval Aviation. Though most Japanese aircraft were characterized by great operating ranges, they had very little in the way of defensive armament and armor. As a result, the more numerous, heavily armed and armored American aircraft were able to develop techniques that nullified the advantages of the Japanese aircraft. Although there were delays in engine development, several new competitive designs were developed during the war, but industrial weaknesses, lack of raw materials and disorganization due to Allied bombing raids hampered their mass-production. Furthermore, the IJN didn't have an efficient process for rapid training of aviators, as two years of training were usually considered necessary for a carrier flyer. Therefore, they weren't able to effectively replace seasoned pilots lost through attrition following their initial successes in the Pacific campaign. The IJN pilots' later inexperience was especially evident during the Battle of the Philippine Sea, when their aircraft were shot down in droves by the American naval pilots in what the Americans later called the "Great Marianas Turkey Shoot." Following the Battle of Leyte Gulf, the Japanese Navy increasingly opted towards deploying aircraft in the kamikaze role.
Towards the end of the conflict, several competitive plane designs were developed, such as the 1943 Shiden, but such planes were produced too late and in insufficient numbers (415 units for the Shiden) to affect the outcome of the war. Radical new plane designs were also developed, such as the canard design Shinden, and especially jet-powered aircraft such as the Nakajima Kikka and the rocket-propelled Mitsubishi J8M. These jet designs were partially based on technology received from Nazi Germany, usually in the form of a few drawings only, Kikka being based on the Messerschmitt Me 262 and the J8M on the Messerschmitt Me 163), so Japanese manufacturers had to play a key role in the final engineering. These developments also happened too late in the conflict to have any influence on the outcome. The Kikka only flew once before the end of the war.
Japan had by far the most varied fleet of submarines of World War II, including manned torpedoes (Kaiten), midget submarines (Ko-hyoteki, Kairyu), medium-range submarines, purpose-built supply submarines (many for use by the Army), long-range fleet submarines (many of which carried an aircraft), submarines with the highest submerged speeds of the conflict (Senkou I-200), and submarines that could carry multiple bombers (World War II's largest submarine, the Sentoku I-400). These submarines were also equipped with the most advanced torpedo of the conflict, the Type 95 torpedo, a 21" (533 mm) version of the famous 24" (610 mm) Type 91.
A plane from one such long-range fleet submarine, I-25, conducted what is still the only aerial bombing attack on the continental United States when Warrant Flying Officer Nobuo Fujita attempted to start massive forest fires in the Pacific Northwest outside the town of Brookings, Oregon on September 9th, 1942. Other submarines undertook trans-oceanic missions to German-occupied Europe, such as I-30, I-8, I-34, I-29 and I-52, in one case flying a Japanese seaplane over France in a propaganda coup. In May 1942, Type A midget submarines were used in the Attack on Sydney Harbour, and the Battle of Madagascar.
Overall, despite their technical prowesses, Japanese submarines were relatively unsuccessful. They were often used in offensive roles against warships (per Mahanian doctrine), which were fast, maneuverable and well-defended compared to merchant ships. In 1942, Japanese submarines managed to sink two fleet carriers, one cruiser, and a few destroyers and other warships, and damage several others. They were not able to sustain these results afterwards, as Allied fleets were reinforced and started using better anti-submarine tactics. By the end of the war, submarines were instead often used to transport supplies to island garrisons. During the war, Japan managed to sink about 1 million tons of merchant shipping (184 ships), compared to 1.5 million tons for Britain (493 ships), 4.65 million tons for the US (1079 ships) and 14.3 million tons for Germany (2840 ships).
Early models were not very maneuverable under water, could not dive very deep, and lacked radar. Later in the war, units fitted with radar were in some instances sunk due to the ability of US radar sets to detect their emissions. For example, Batfish (SS-310) sank three such in the span of four days. After the end of the conflict, several of Japan's most original submarines were sent to Hawaii for inspection in "Operation Road's End" (I-400, I-401, I-201 and I-203) before being scuttled by the U.S. Navy in 1946 when the Soviets demanded access to the submarines as well.
At the end of the Second World War, numerous Special Attack Units (Japanese: 特別攻撃隊, tokubetsu kōgeki tai, also abbreviated to 特攻隊, tokkōtai) were developed for suicide missions, in a desperate move to compensate for the annihilation of the main fleet. These units included Kamikaze ("Divine Wind") bombers, Shinyo ("Sea Quake") suicide boats, Kairyu ("Sea Dragon") suicide midget submarines, Kaiten ("Turn of Heaven") suicide torpedoes, and Fukuryu ("Crouching Dragon") suicide scuba divers who would swim under boats and use explosives mounted on bamboo poles to destroy both the boat and themselves. Kamikaze planes were particularly effective during the defense of Okinawa, in which 1465 planes were expended to damage around 250 American warships.
A considerable number of Special Attack Units were built and stored in coastal hideouts for the desperate defense of the Home islands, with the potential to destroy or damage thousands of enemy warships.
Following Japan's surrender to the Allies at the conclusion of World War II, and Japan's subsequent occupation, Japan's entire imperial military was dissolved in the new 1947 constitution which states, "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." Japan's current navy falls under the umbrella of the Japan Self-Defense Forces (JSDF) as the Japan Maritime Self-Defense Force (JMSDF).