Imperial Japanese Navy in World War II

The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the most powerful navy in the world.^[3] During the first years of the war the Imperial Japanese Navy dominated the Western Pacific. However, after a series of defeats it lost control of the Western Pacific and collapsed by the end of the war. The naval air service was one of the most potent air forces in the world before its destruction in World War II. Nearly all of its ships were sent to the bottom of the sea by the war's end.

Warships

Battleships

Yamato, the heaviest battleship in history, in 1941.

Japan continued to attribute considerable prestige to battleships (戦艦　Senkan) and endeavoured to build the largest and most powerful ships of the period. Yamato, the heaviest and most heavily armed battleship in history, was launched in 1941.^[4]

The second half of World War II saw the last battleship duels. In the Battle of Guadalcanal on 15 November 1942, the U.S. battleships USS South Dakota and Washington fought and destroyed the Japanese battleship Kirishima, but only after South Dakota had sustained heavy damage. In the Battle of Leyte Gulf on 25 October 1944 six battleships, led by Rear Admiral Jesse Oldendorf of the U.S. 7th Fleet, fired upon and claimed credit for sinking Vice 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 battleships, and probably only Yamashiro was the target of their fire.

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 Vice Admiral Takeo Kurita and the fight by American destroyers and destroyer escorts saved the American escort carriers of "Taffy 3" from destruction by the gunfire of Yamato, Kongō, Haruna, and Nagato and their cruiser escort. Miraculously for the Americans, only one escort carrier, 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.^[5] As a result of the changing technology, plans for even larger battleships, such as the Japanese Super Yamato-class battleships, were cancelled.

Aircraft carriers

The Shōkaku shortly after completion in August 1941.

In the 1920s, the Kaga (originally laid down as a battleship) and a similar ship, the Akagi (originally laid down as a battlecruiser) were converted to aircraft carriers (航空母艦 Kōkūbokan) to satisfy the terms of the Washington Naval Treaty.^[6] From 1935–1938, Akagi and Kaga received extensive rebuilds to improve their aircraft handling capacity.^[6]

Japan put particular emphasis on aircraft carriers. The Imperial Japanese Navy started the Pacific War with 10 aircraft carriers,^[7] 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.^[8] 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 IJN 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 only Japanese carrier with an armored flight deck and first to incorporate a closed hurricane bow. All three mid-war designs were sunk in 1944, with Shinano and Taihō being sunk by U.S. submarines, and Hiyō by air attacks.

Destroyers

Japanese World War II destroyers (駆逐艦 Kuchikukan) included some of the most formidable destroyers of their day. This came as a nasty surprise to the Allies, who had generally underestimated Japanese technical capabilities. The Japanese had reassessed their naval needs in the mid-1920s and, placing an emphasis on ship and weapons technology and night fighting expertise, developed a completely new destroyer design. Subsequent development from one destroyer class to the next was not, however, a smooth progression. Aside from the usual changes arising from experience, serious design faults also came to light and naval treaties imposed restrictions. As a result, the early "Special Type" destroyers required significant changes and the specifications of subsequent classes was reduced in one way or another. Naval treaties were later abrogated in 1937 and so destroyer development continued without regard to limits.

Generally speaking, the Imperial Japanese Navy (IJN) requirements gave rise to warships that were substantially larger than their European or American equivalents. In the early war years, their advantages were exploited against the often second rate and poorly coordinated Allied ships stationed in the region such as at the IJN victory in Battle of the Java Sea. The Japanese did not, however, continue to install new technology, such as radar, to match their opponents, and destroyer numbers were eroded steadily. The Japanese emphasis on fleet destroyers had neglected the need for large numbers of escort vessels to defend critical merchantmen, a need learnt by both the Royal Navy and the United States Navy in the Battle of the Atlantic. In recognition that quantity was as important as quality in some roles, design policy was therefore modified to produce units that were easier to build and operate. Despite this, Japan's destroyer force was halved by the end of the war. The survivors were given to the Allies.

Naval aviation

Planes from the Japanese aircraft carrier Shōkaku preparing the attack on Pearl Harbor.

Japan began the war with a highly competent naval air force designed around some of the best airplanes in the world: the A6M 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 the world's best flying boat.^[9] 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.^[10] 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.^[11]

As the war progressed, 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.^[12] 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,^[13] 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 did not have an efficient process for rapid training of aviators, as two years of training were usually considered necessary for a carrier flyer. Therefore, they were not able to effectively replace seasoned pilots lost through combat attrition following their initial successes in the Pacific campaign.^[12] The inexperience of IJN pilots who were trained in the later part of the war 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.

Japan's first jet-powered aircraft, the Imperial Japanese Navy's Nakajima J9Y Kikka (1945).

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.^[14] 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.^[15] These developments also happened too late in the conflict to have any influence on the outcome. The Kikka only flew twice before the end of the war.^[16]

Submarines

An Imperial Japanese Navy's I-400-class submarine, the largest submarine type of World War II.

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-201), 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 533 mm (21 in) version of the famous 610 mm (24 in) Type 93.^[17]

A plane from one such long-range fleet submarine, I-25, conducted 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 9, 1942.^[18] 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.^[19] In May 1942, Type A midget submarines were used in the attack on Sydney Harbour and the Battle of Madagascar.

Overall however, Japanese submarines were relatively unsuccessful.^[20] 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 (Yorktown and Wasp), one cruiser, and a few destroyers and other warships, and damage several others (aircraft carrier Saratoga).^[20] 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 (170 ships) with her 184 submarines, compared to 1.5 million tons for Britain (493 ships), 4.65 million tons for the US (1079 ships)^[21] and 14.5 million tons for Germany (2,000 ships) with her 1,000 U-Boats.^[20]

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, USS Batfish sank three such in the span of four days. After the end of the conflict, several of Japan's most innovative and advanced 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.^[18]

Special Attack Units

A kamikaze Zero, about to hit the USS Missouri 11 April 1945.

At the end of World War II, 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.^[22] These units included Kamikaze ("Divine Wind") bombers,^[22] Shinyo ("Sea Quake") suicide boats,^[23] Kairyu ("Sea Dragon") suicide midget submarines,^[24] Kaiten ("Turn of Heaven") suicide torpedoes,^[23] 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.^[23] Kamikaze planes were particularly effective during the defense of Okinawa, in which about 2,000 planes were sent to sink 34 warships and damage around 364.^[25]

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.^[23]

Navy Land Forces

The Imperial Japanese Navy Land Forces of World War II originated with the Special Naval Landing Forces, and eventually consisted of the following:

• Special Naval Landing Force or Rikusentai or kaigun rikusentai or Tokubetsu Rikusentai: the Japanese Marines
• The Base Force or Tokubetsu Konkyochitai provided services, primarily security, to naval facilities
• Defence units or Bobitai or Boei-han: detachments of 200 to 400 men.
• Guard forces or Keibitai: detachments of 200–500 men who provide security to Imperial Japanese Navy facilities
• Pioneers or Setsueitai built naval facilities, including airstrips, on remote islands.
• Naval Civil Engineering and Construction Units, or Kaigun Kenchiku Shisetsu Butai
• The Naval Communications Units or Tsushintai of 600–1,000 men to provide basic naval communications and also handled encryption and decryption.
• The Tokkeitai Navy military police units were part of the naval intelligence armed branch, with military police regular functions in naval installations and occupied territories; they also worked with the Imperial Japanese Army's Kempeitai military police, the Keishicho civil police and Tokko secret units in security and intelligence services.

Personnel Strength

• December 1941 — 291,359 including 1,500 pilots
• July 1945 — 1,663,223

See also

• List of Japanese Navy ships and war vessels in World War II
• Imperial Japanese Navy order of battle 1941

Notes

References

• Evans, David C; Peattie, Mark R (1997). Kaigun: strategy, tactics, and technology in the Imperial Japanese Navy, 1887–1941. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-192-7. 
• Peattie, Mark R (2007). Sunburst: The Rise of Japanese Naval Air Power, 1909–1941. Annapolis, Maryland: Naval Institute Press. ISBN 1-61251-436-7. 
• Stille, Mark (2014). The Imperial Japanese Navy in the Pacific War. Osprey Publishing. ISBN 1-47280-146-6. 

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