Imperial Japanese Navy in World War II
|Imperial Japanese Navy
warships in World War II 
|Number of units|
The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the third most powerful navy in the world. During the first six months of the war, the Navy was undefeated in every battle. 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.
At the beginning of the Pacific War, the strategy of the Imperial Japanese Navy was underpinned by several key assumptions. The most fundamental was that, just as the Russo-Japanese war had been decided by the naval Battle of Tsushima (May 27–28, 1905) the war against the United States would be decided by a single decisive naval battle, or Kantai Kessen. This great naval clash would be determined by the big guns aboard battleships, and this conviction was shared by both the Japanese and the American naval leaders alike. All other arms of the navy were to be dedicated to supporting the battleships when they met the Americans in battle. The Japanese assumed that at the start of any conflict, they would quickly seize the largely unprotected American-held Philippines. This would force the United States to undertake a drive across the Pacific to retake them. Consequently, the great decisive clash would take place somewhere in the western Pacific where the Japanese decided the time was right to stop the American advance.
It was also clear to the Japanese that in order to win the decisive battle they would have to make up for numerical disadvantage. The Japanese acknowledged that they would never have the industrial capacity to create a navy that was equal in size to the United States, however, as they were planning on being on the defensive, they calculated that they had to have only 70 percent of the strength of the United States Navy to be in a position to achieve victory. This assumption was built on two pillars, both became driving forces in Japanese naval construction, tactical development, and training between the wars. The first was that the Japanese would had to have the weapons and tactics to inflict severe attrition on the US Pacific Fleet before the decisive battle, which would bring the Japanese to at least parity. Once at rough parity, Japanese naval units with superior speed and capable of hitting at ranges beyond the reach of the Americans and crewed by expertly trained personnel, would win the day.
The Imperial Japanese Navy thought that they would fight a limited war in which Japan would seize key objectives and then create a defensive perimeter to defeat Allied counterattacks, which in turn would lead to a negotiated peace. The initial period of the war was divided into two operational phases. The First Operational Phase was further divided into three separate parts; during these, the major objectives of the Philippines, British Malaya, Borneo, Burma, Rabaul and the Dutch East Indies would be occupied. The Second Operational Phase would entail further expansion into the South Pacific by seizing eastern New Guinea, New Britain, the Fiji Islands, Samoa, and strategic points in the Australian area. In the Central Pacific, Midway would be taken as well as the Aleutian Islands in the Northern Pacific. Seizure of these key areas would provide a defensive perimeter and depth to deny the Allies staging areas from which to mount a counteroffensive.
First operation phase
To the surprise of the Japanese, the First Operational Phase went according to plan with extremely light losses, no ship larger than a destroyer was sunk. The invasion of Malaya and the Philippines began in December 1941. Japanese Land based naval bombers achieved notable success on December 10, when operating from bases in Indochina, they sank the British capital ships Prince of Wales and Repulse. The island of Guam was seized on December 8 after token American resistance. The British Gilbert Islands were seized on December 9 and 10. The only temporary setback for the Japanese was the failure of the first attempt to seize Wake Island on December 11. In response, a carrier division from the Pearl Harbor attack force was diverted to Wake island for the a second attempt on December 22, which was this time around successful. The British the fortress of Singapore also surrendered on February 15.
Allied naval opposition to the Imperial Japanese Navy during the First Operational Phase was sporadic and ineffective. In the first major surface engagement of the war on February 27 at the Java Sea, an Allied naval force was defeated by a Japanese one of similar size. Following its debut at Pearl Harbor, the Kido Butai supported the capture of Rabaul in January 1942 and the Dutch East Indies in February. The only problem encountered by the Japanese during the First Operational Phase was the failure to occupy the Philippines on schedule. However, with no expectation of reinforcement, the fall of the Philippines was only a matter of time and the remaining American and Filipino forces surrendered in early May 1942. The last major operation of the First Operational Phase was the Combined Fleet's raid into the Indian Ocean. This significant operation included five carriers to neutralize the Royal Navy's Eastern Fleet and a task force built around heavy cruisers to attack shipping in the Bay of Bengal. The operation began in April with the Japanese delivering heavy attacks against British bases at Colombo and Trincomalee. Japanese carrier aircraft also caught and sank a light carrier HMS Hermes and the two heavy cruisers HMS Dorsetshire and HMS Cornwall, but were unable to locate and destroy the main British fleet. The Japanese cruiser raiding force wreaked havoc with British shipping in the Bay of Bengal, however, the entire operation was a strategic dead end since it was only a temporary projection of power that could not be sustained and served only to put more strain on the Japanese carrier force.
Second operation phase
The ease with which the Japanese accomplished its First objectives led to the severe underestimation of the enemy and the resulted failure to concentrate the Imperial Japanese Navy's superior forces at key places and times. As a result, the critical months of May and June 1942 saw the IJN lose both its offensive power and the initiative. The Second Operational Phase was planned to expand Japan's strategic depth by adding eastern New Guinea, New Britain, the Aleutians, Midway, the Fiji Islands, Samoa, and strategic points in the Australian area. However, the Naval General Staff, the Combined Fleet, and the Imperial Army, all had different views on the next sequence of operations. The Naval General Staff advocated an advance to the south to seize parts of Australia, however, the Imperial Japanese Army declined to contribute the forces necessary for such an operation, which quickly led to the abandonment of the concept. The Naval General Staff still wanted to cut the sea links between Australia and the United States by capturing New Caledonia, Fiji, and Samoa. Since this required far fewer troops, on March 13 the Naval General Staff and the Army agreed to operations with the goal of capturing Fiji and Samoa. The Second Operational Phase began well when Lae and Salamaua located on eastern New Guinea were captured on March 8. However, on March 10, American carrier aircraft attacked the invasion forces and inflicted considerable losses. The raid had major operational implications since it forced the Japanese to stop their advance in the South Pacific and this was to be the last of the uninterrupted victories for the Japanese until the Combined Fleet provided the means to protect future operations from American carrier attack.
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. However, they only managed to complete Yamato and Musashi, while the third member of the class Shinano was converted to an aircraft carrier and sunk before completion. As a result of the changing technology as well as unexpected heavy losses in aircraft carriers in 1942, plans for even larger battleships, such as the Japanese Super Yamato-class battleships, were cancelled.
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 sunk the Japanese battleship Kirishima, at the cost of moderate topside damage to South Dakota. For the Battle of Leyte Gulf the Japanese had to use their battleships as the main combatants, due to the heavy losses in their carrier air wings suffered in the earlier Battle of the Philippine Sea which relegated the carriers to decoys. 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 torpedo attacks from destroyers before being brought under fire by Oldendorf's battleships, and probably only Yamashiro was the target of their fire.
Thanks to the Japanese carriers successfully decoy role, the Battle off Samar on 25 October 1944 during the Battle of Leyte Gulf showed battleships could still be useful. However the persistent American air attacks coupled with 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. Only the fast battleships (formerly battlecruisers) of the Kongo class saw much action due to their speed, while the slower and heavier battleships were held in reserve for a decisive engagement of battleships versus battleships which never really happened. Yamato and Musashi were sunk by air attacks long before coming in gun range of the American fleet.
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. 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. 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. Nonetheless the Japanese initially had the upper hand over the American and British, by grouping all of their fleet carriers into a single unit known as the 1st Air Fleet or Kidō Butai ("Mobile Force"). In the Kidō Butai, the two Shōkaku-class carriers were superior to any carrier in the world, until the wartime appearance of the American Essex class.
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), robbing them of a strategic offensive capability. The IJN consequently undertoock an ambitious set of projects to convert commercial and military vessels into 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. One exception was 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. The IJN also attempted to build a number of fleet carriers called the Unryū-class, mostly based on the older Hiryū design rather than the newer Shōkaku or Taihō for the sake of reducing construction cost and time. Most carriers were still under construction or cancelled by the end of the war, while the few completed ships never embarked air groups due to severe shortages of carrier-qualified aircrew.
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, often well-equipped with heavy torpedo armament for surface engagements but with less emphasis on anti-aircraft or anti-submarine armament. 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 the 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 in the latter half of the Pacific War. The Japanese emphasis on capable but expensive fleet destroyers had neglected the need for large numbers of cheaper escort vessels (destroyer escorts or frigates) 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.
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. 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 land-based 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 progressed, the Allies found weaknesses in Japanese naval aviation. Though most Japanese aircraft were characterized by great operating range and agility, 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. The early carrier versus carrier naval battles in 1942 such as Coral Sea and Santa Cruz Island were tactical victories for the IJN but they suffered disproportionately high aircrew losses compared to the US Navy. 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. 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.
Although there were delays in engine development, several new competitive aircraft designs were developed during the war, but industrial weaknesses, lack of raw materials and disorganization due to Allied bombing raids hampered their mass-production. 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 twice 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-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.
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. 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.
|Sinking of merchant shipping,
during World War II.
|United States||1,079||4.65 million|
Overall however, Japanese submarines were relatively unsuccessful. They were often used in offensive roles against warships (in accordance with 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 (Juneau), and a few destroyers and other warships, and damage several others (aircraft carrier Saratoga). They were not able to sustain these results afterwards, as Allied fleets were reinforced and started using better anti-submarine tactics including those learned from the Battle of the Atlantic. 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) and 14.5 million tons for Germany (2,000 ships) with 1,000 U-Boats.
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.
Special Attack Units
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. 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 about 2,000 planes were sent to sink 34 warships and damage around 364.
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.
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.
- December 1941 — 291,359 including 1,500 pilots
- July 1945 — 1,663,223
- List of Japanese Navy ships and war vessels in World War II
- Imperial Japanese Navy order of battle 1941
- List of ships of the Second World War
- Evans & Peattie 1997, p. 496.
- Jentschura, "Warships of the Imperial Japanese Navy, 1869–1945", p.25-60, p.79-87, p.104-113, ISBN 978-0-87021-893-4
- Stille 2014, p. 8.
- Stille 2014, p. 12.
- Evans & Peattie 1997, p. 141.
- Evans & Peattie 1997, p. 143.
- Stille 2014, p. 29.
- Stille 2014, p. 30.
- Stille 2014, p. 31.
- Evans & Peattie 1997, p. 295 & 370.
- Evans & Peattie 1997, pp. 379–380.
- Evans & Peattie 1997, p. 315.
- Evans & Peattie 1997, p. 323.
- "In many ways the Japanese were in the forefront of carrier design, and in 1941, the two Shōkakus — the culmination of prewar Japanese design — were superior to any carrier in the world then in commission" Evans, Kaigun p323
- "For speed and maneuverability, for example the Zero was matchless; for range and speed few bombers surpassed the Mitsubishi G3M, and in the Kawanishi H8K, the Japanese navy had the world's best flying boat" Evans, Kaigun, p312
- "by 1941, by training and experience, Japan's naval aviators were undoubtedly the best among the world's three carrier forces" Evans, Kaigun, p325
- Peattie 2007, p. 169.
- Evans & Peattie 1997, p. 314.
- Evans & Peattie 1997, p. 313.
- The Illustrated Directory of Fighters Mike Spick p.219
- Japan and Germany in the modern world by Bernd Martin p.280
- The origins of Japanese trade supremacy: development and technology in Asia by Christopher Howe p.313ff 
- Evans & Peattie 1997, p. 266.
- Cold War submarines: the design and construction of U.S. and Soviet submarines by Norman Polmar, Kenneth J. Moore p.246-247  Cite error: Invalid
<ref>tag; name "Polmar" defined multiple times with different content (see the help page).
- Japanese submarines, p70
- Evans & Peattie 1997, p. 497.
- Tonnage Sunk, Pacific 1941 – 1945
- The Divine Wind: Japan's Kamikaze Force in World War II Rikihei Inoguchi, Tadashi Nakajima, Roger Pineau p.150 
- Making sense of suicide missions Diego Gambetta p.7ff
- The Japanese submarine force and World War II Carl Boyd, Akihiko Yoshida p.34 
- The Naval Institute historical atlas of the U.S. Navy Craig L. Symonds, William J. Clipson p.186 
- 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.