IJN - Imperial Japanese Navy ( Nihon Kaigun ) ==========================================================================



The evolution of Japanese naval power in the five decades leading up to World War II was one of the most significant trends of the 20th Century. The Imperial Fleet was founded in the wake of the Meiji Restoration in 1868, which unified Japan. Although they lacked the infrastructure of Europe or the United States, over the next forty years the Japanese managed to construct a navy that was strong enough to decisively defeat a regional power, China, as well as a great European power, Russia.


The Imperial Japanese Navy (IJN), officially Navy of the Greater Japanese Empire ( Dai-Nippon Teikoku Kaigun or Nippon Kaigun), was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes. It was the third largest navy in the world by 1920 behind the Royal Navy and United States Navy,. It was supported by the Imperial Japanese Navy Air Service for aircraft and airstrike operation from the fleet. It was the primary opponent of the Allies in the Pacific War.

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.

Following the attempts at Mongol invasions of Japan by Kubilai Khan in 1274 and 1281, Japanese wakō became very active in plundering the coast of the Chinese Empire.

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).

In 1853 and 1854, U.S. Navy Commodore Matthew Perry made a demonstration of force with the newest steam warships of the U.S. Navy. Perry finally obtained the opening of the country to international trade through the 1854 Convention of Kanagawa. This was soon followed by the 1858 "unequal" U.S.-Japan Treaty of Amity and Commerce, which allowed the establishment of foreign concessions, extra-territoriality for foreigners, and minimal import taxes for foreign goods.

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.

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. 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 of Military Affairs (also known as the Army-Navy 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.

Japan had desired to be the most powerful nation in the Far East since the 1890s. As part of that plan, Japan had to expand to acquire areas that were rich in natural resources not available in Japan and to form a protective outer ring away from the home islands. In need of raw materials and new markets, Japan fought China in the Sino-Japanese War in 1894-95. Fought in Korea and Manchuria, the Imperial Army and Imperial Navy won numerous victories, forcing China to sue for peace, in which China ceded Korea and Formosa and paid a large indemnity. In 1905, ships of the Combined Fleet, under the command of Fleet Admiral Heihachiro Togo, sailed from Sasebo to engage Russia’s Baltic Fleet. Admiral Togo’s victory during the Battle of Tsushima is a classic in naval history. With victories over the Russians and Chinese in the late 1890s/early 1900s, Japan had obtained Formosa, Korea, the Kuril Islands, and parts of Manchuria. As an ally at the end of World War I, Japan was mandated from Germany possession of the Marshall Islands, the Caroline Islands, and the Mariana Islands.

Prior to the First World War the Imperial Japanese Navy was very dependent on foreign suppliers for its arms and equipment. Many of the prominent overseas warship builders supplied vessels to the Imperial Navy with the majority being built in British yards. In addition, the Japanese Navy acquired many ships as prizes in both the war with China and the Russo-Japanese War. This combination allowed a very rapid expansion of the fleet while also affording ample opportunities to study foreign construction methods and techniques. Destroyers were purchased mainly from Yarrows and Thonnycroft, leaders in destroyer design at the time. Later, some units were built in Japan through licensing agreements. Ships such as the Fusō, Kongō and the Hiei were built in British shipyards specifically for the Imperial Japanese Navy. Private construction companies such as Ishikawajima and Kawasaki also emerged around this time.

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 , who happened to be 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 ("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.

Shimose powder was a type of gunpowder developed by the Japanese chemist Shimose Masachika (1860-1911). The powder was used by the Imperial Japanese Navy from 1893, and played an important role in the Japanese victory in the 1905 Russo-Japanese War[1]. The Shimose powder formulation was derived from that of the smokeless powder developed by the French inventor Paul Vielle in 1884. The powder brought great precision to Japanese gunnery: Shimose powder was also used as the explosive in Japanese torpedoes such as the Type 93.

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 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", in which it commissioned 109 warships, for a total of 200,000 tons, and increased its Navy personnel from 15,100 to 40,800.

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 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 to Japan (October 1904) and then assembled 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:

Japan entered World War I on the side of the Allies, against Imperial Germany and Austria-Hungary, as a natural prolongation of the 1902 Anglo-Japanese Alliance.

In the Battle of Tsingtao, the Japanese Navy seized the German naval base of Tsingtao. During the battle, beginning on 5 September 1914, the Japanese seaplane carrier 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

As Japanese shipbuilding capacity expanded and the ship constructors gained more experience, original designs were built. Initially these were still based on British practice. The break from British design dominance occurred in 1916 when the Navy issued specifications for new First and Second Class destroyers. These new vessels, the Minekaze and Momi classes, departed from the traditional British layout, adopting a design that owed much to German ideas.

The design of the Minekaze class destroyers was based off of German destroyer practices, as opposed to the British designs which had previously been the norm. Ranked as first class destroyers, the Minekaze class had an extended forecastle which was seperated by a well from the bridge to allow space for torpedo tubes in between, as well as decrease the affects of heavy seas. The elevation of the guns differentiated the Minekaze type from the other destroyers in the fleet at the time, as they were placed higher than the main deck along her entire length.

Thirty-six ships were eventually laid down and completed of the Minekaze class F-41 design from 1919 to 1922. The Momi class destroyers were considered second class versions of the Minekaze design.

The Momi class destroyers were entirely of Japanese design, but borrowed heavily from the concepts of the German based Minekaze destroyers. The ships initially had listing problems during high speed turns, which later was corrected by widening the beam and bring up the waterline. The Momi destroyers operated well in groups of two to four and were recognized as the main attack force used by the Imperial Navy of the time period.

Responding to the American naval construction plan approved in August 1916, which called for "a fleet second to none," the Japanese accelerated the progress of an earlier adopted plan, called "8/8," which was to lead to the construction of eight battleships and eight battle cruisers. The Japanese considered this program vital to strengthen their position in the Far East and secure it militarily, and to counter growing opposition from the United States.

By 1920 Tokyo had the third largest fleet in the world. Despite continuing industrial inferiority — and with an economy that was one-ninth the size of America and heavily dependent on imports of raw materials — Japan was sufficiently powerful to directly challenge the US Navy in the Pacific.

With the agreements of the Washington Naval Treaty of 1922, Japan was forced to amend her construction plans. Nine battleships and three battle cruisers were scrapped on the ways as a result of this Treaty. Two vessels, battleship KAGA and battle cruiser AKAGI, were spared and converted into aircraft carriers.

In 1934, Japanese League of Nations delegates were angered by sanctions imposed on their country by that organization over the Manchurian Affair and Japan withdrew from that august body and renounced all naval treaty obligations. Soon after, long term plans were considered along with the possible actions and reactions of foreign nations, particularly potential adversaries such as the United States. Along with the preliminary design of the future YAMATO class, plans were drawn up that, hopefully, would allow Japan's pace for expansion to remain unhindered without triggering a war with America until the fleet was ready. The Japanese Imperial Navy attempted to build ships with which it was hoped "peace" could be maintained throughout the Pacific Rim by intimidation alone. The cornerstone of this belief was the battleship YAMATO armed with the highly secret 18-inch gun.

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 alienated the United States, which was seen as a rival of Japan for control of the Pacific.


As a military force, the Imperial Japanese Navy was a relatively new creation. In the formative years before the turn of the century, in order to catch up with the West, Japan relied heavily of foreign assistance. The IJN was organized and trained by the British Royal Navy and many of the ships came from British yards. A military alliance was in effect between Great Britain and Japan which was entered into by both parties to counter Russian ambitions in the Far East. Japan honored this agreement and declared war on Germany during the First World War. Japan seized all of the German protectorates in the Pacific as her contribution to the war effort but did not send any troops to France. The Japanese Navy was present in European waters but not to the extent that was requested. After the Great War Japan emerged as the most powerful naval force in the Pacific. Tensions increased steadily between the United States and Japan and, under pressure from Washington, Great Britain did not renew the mutual assistance alliance with Japan. Japan's political isolation increased through the twenties and become almost total once she embarked on the military misadventure in China. The effect of these events upon the Japanese Naval constructors was highly detrimental. While their experience was limited, they were confronted with a very rapidly changing technology, increasing sizes of ships, and were "out of the loop" with no free exchange of technical knowledge with their peers in other nations. It is for this reason that Japanese ships have their unique "look", quite unlike any other navy. Japanese designers had to come up with original solutions with no outside input. Some were extraordinarily successful, some were not. Calculations of new designs were also affected and there may well have been a very large portion of "honest error" in some of the excess tonnage results.

This could certainly be true in the case of the first large ships, the TAKAOs. After that, it would be self-perpetuating as the Navy would be reluctant to give up the power gained by accepting inferior designs. Deception and duplicity would then be a factor in the public pretense that the NACHI and MOGAMI class ships were in compliance with the treaty limitations. They were not, and the Navy knew it, but was unwilling to sacrifice anything in succeeding designs in order to bring them into compliance.

The political emergence of the Imperial Japanese Navy between 1868 and 1922 contradicts the popular notion that the navy was a 'silent,' apolitical service. Politics, particularly budgetary politics, became the primary domestic focus — if not the overriding preoccupation — of Japan's admirals in the prewar period. As the Japanese polity broadened after 1890, navy leaders expanded their political activities to secure appropriations commensurate with the creation of a world-class blue-water fleet.

The Imperial Japanese Navy worked the Japanese body politic more successfully than almost any other organization between 1868 and 1918. It did so to transform itself from a motley collection of ships into the third most powerful navy in the world. But it also strengthened or at least further legitimated parliamentary democracy, demonstrated the potential political effectiveness of mass propaganda and pageantry, fostered nationalism, and enlarged Japan's empire toward the South Seas in perception as well as reality.

The navy's sophisticated political efforts included lobbying oligarchs, coercing cabinet ministers, forging alliances with political parties, occupying overseas territories, conducting well-orchestrated naval pageants, and launching spirited propaganda campaigns. These efforts succeeded: by 1921 naval expenditures equaled nearly 32 percent of the country's total budget. The navy made waves at sea and on shore, and in doing so significantly altered the state, society, politics, and empire in prewar Japan.

Inter-service rivalry over budget allocations between the Japanese Imperial Navy and the Imperial Army played a crucial role in the genesis of World War Two in the Pacific. The adoption of a nanshin ("southward advance") strategy by the Navy may be explained as an attempt to maximize its budget leading directly to the attack on Pearl Harbor in 1941.

The Japanese navy emulated foreign practices and evolved innovative concepts of its own. Tokyo looked to the world’s most powerful fleet—the Royal Navy—as the model for modernization. Japan purchased the best naval technology and to build an impressive domestic arms industry. By the early 20th century, this process yielded a fleet that was better organized, trained, and equipped than any other in the region.

When Japan was locked in combat with Russia in 1905 and looked for asymmetric ways to defeat the superior Russian navy and started acquiring submarines. Their first five submarines were purchased from the United States. After the war with Russia, Japan developed its own submarines and continued to improve them, developing numerous types including seaplane carriers, mine warfare submarines, and midget submarines [By 1941 Japan had 65 fleet submarines, and the US Pacific Fleet had only 23].

The Washington Treaty of 1922 initially limited the Japanese to 315,000 tons of capital ships, 60% of the 525,000 tons allowed to the United States. The United States and Britain had to reduce their navies (the United States scrapped 15 battleships and cruisers that had been under construction) while the Japanese had to build up to get to their “limitation.” With the stroke of a pen, Japan reduced the size of the US Navy while being allowed to increase the size of its own navy. This was followed by the 1930 London Treaty that further restricted Japanese naval strength by limiting the Japanese to 108,400 tons of heavy cruisers, 60.23% of the American heavy cruiser force, to 100,450 tons of light cruisers, 70% of the American allowance, and 52,700 tons of submarines.

The Sino-Japanese and Russo-Japanese wars spawned a unique Japanese approach to naval thought that dominated strategic and tactical discussion up to World War II. Forbidden by treaty from matching America quantitatively, Japan sought to exploit operational and technological niches to inflict disproportionate damage. Under the rubric of “using a few to conquer many,” the Japanese developed comparative advantages such as long-range torpedo combat, night operations by surface units, and a tactic of outranging the U.S. fleet with subsurface, surface, and air forces. The Imperial Navy also designed and produced weapons needed to implement its strategy. During the early 1930s it deployed the first oxygen-propelled (Type 93) torpedo torpedo, whose range, speed, and payload far exceeded American and British models. In 1940 it fielded the Mitsubishi A6N “Zeke,” the world’s foremost carrier-based fighter.

While Japan lagged behind the United States and Great Britain in high-technology systems like radar, it built less-advanced sensors, including superior optics and searchlights. By 1940 the Japanese were much the equal of their British and American foes in training, technological innovation, and tactical proficiency.

The Imperial Japanese Navy was a pioneer in naval aviation, having commissioned the world's first built-from-the-keel-up carrier, the 'Hosho'. Throughout the 1920s and 1930s, it experimented with its carriers, perfecting their design and construction. As result, by 1941 it possessed a fantastically effective naval aviation force.

In 1907, the same year the US Navy began working on its Orange Plan for rescuing the Philippines from Japan, the United States became for the Japanese navy the "budgetary enemy." Despite the fact that Japan had been an ally during World War I, American war planning in the interwar years focused on war with Japan, and Japanese planning focused on the United States. In June 1940 Japan sought and received the French Vichy government's permission to land forces in French Indochina. Japanese Prime Minister Matsuoka Yôsuke announced the idea of the Greater East Asia Co-Prosperity Sphere (Dai-to-a Kyoeiken, variants: Dai Toa Kyoeiken, Daitoa Kyoeiken, Daitoa="Greater East Asia", Kyoeiken="Co-Prosperity Sphere") in August 1940. In September 1940 Japanese troops started occupying northern parts of French Indochina.

President Franklin D. Roosevelt’s administration reacted by placing an embargo on steel and scrap iron from the United States, an event the Japanese termed an “unfriendly act.” In July 1941 Japan demanded more Indochinese bases, and when Japan moved to occupy these bases, the United States, Great Britain, and the Netherlands froze Japanese assets. They also imposed an all-out embargo against Japan, including the export of oil. Japan imported all of the oil it used and had now lost access to almost all of its sources.

In August 1941 Japanese war planning increased as the military leaders realized that war with the United States was more likely everyday. In response to the American embargo, the Imperial Staff developed the “Southern Operation,” a plan for capturing the industrial rich Dutch East Indies and Malaya. Japan realized this action would force the United States and Great Britain into war, so the plan also called for seizing the American-held Philippines and Guam and the British possessions of Hong Kong and Burma. Once the southern areas were secured, Japan would occupy strategic positions in the Pacific and fortify them, thus forming a tough defensive perimeter around Japan and its newly acquired resource areas. Once the perimeter was secure, Japan would try to negotiate for peace. The planners thought it would take six months to accomplish all the tasks and had to be free of interference from the American Navy during that time. Yamamoto had the plan for ensuring that the US Pacific Fleet would not interfere for six months.

On December 7, 1941, Japanese navy airplanes raided the Pearl Harbor (Hawaii) base of the United States. The American Pacific fleet was almost completely annihilated. The purpose of this action was to destroy America's main fleet and then secure sea control in the Pacific. On the same day, the Japanese army landed in Malaysia and moved towards Singapore. Japan declared war on Britain and the United States, calling this a "War of Self-Defense and Existence" [Jison Jiei Senso]. The Japanese government named this war the Great East Asian War (Daitowa Senso). After the war, the Americans banned the use of the term Greater East Asian War and therefore it is called the Pacific War (Taiheiyo Senso). Japan claimed that this was a war of self-defense by Japan, and to establish the "Great East Asian Co-Prosperity Sphere" in order to break down the stranglehold of the American and European countries. Germany and Italy also declared war against the United States. For five months after Pearl Harbor, the Imperial Japanese Navy's Combined Fleet moved across the Pacific with virtual impunity.

At the beginning of the Second World War, the Japanese Navy (or, in the Japanese language, Nihon Kaigun, or even Teikoku Kaigun, the Imperial Navy) was arguably the most powerful navy in the world. Its naval aviation corps, consisting of 10 aircraft carriers and 1500 topnotch aviators, was the most highly trained and proficient force of its kind. Its 11 (soon to be 12) battleships were among the most powerful in the world. And its surface forces, armed with the superb 24" Type 93 (Long Lance) torpedo, were incomparable night fighters. How and why this impressive force was eventually crushed by the U.S. Navy is a subject that has fascinated me practically forever.

It's no secret that Japan was, shall we say, 'economically disadvantaged' in her ability to wage war against the Allies. However, the sheer, stunning magnitude of this economic disparity has never ceased to amaze me. In retrospect, it is difficult to comprehend how Japan's leadership managed to rationalize their way around the economic facts when they contemplated making war on the U.S. After all, these were not stupid men. In the end, however, the Tojo government chose the path of aggression, compelled by internal political dynamics which made the prospect of a general Japanese disengagement in China (which was the only means by which the American economic embargo would have been lifted) too humiliating a course to be taken. Consequently, the Japanese embarked on what can only be described as a suicidal venture, against an overwhelmingly large foe. However, their greatest mistake was not just disregarding the economic muscle which lay partially dormant on the other side of the Pacific. In actuality, their chief error lay in misreading the will of the American people. When the American giant awoke, it did not lapse into despair as a result of the defeats that Japan had inflicted upon it. Rather, it awoke in a rage, and applied every ounce of its tremendous strength with a cold, methodical fury against its foe. The grim price Japan paid -- 1.8 million military casualties, the complete annihilation of its military, a half million or so civilians killed, and the utter destruction of practically every major urban area within the Home Islands -- bears mute testimony to the folly of its militarist leaders.

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", 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.

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.

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 1921 it launched the Hōshō, the first purpose-designed aircraft carrier in the world to be completed, and subsequently developed a fleet of aircraft carriers second to none.

In keeping with its doctrine, the Imperial Navy was the first navy in the World to mount 14-in (356 mm) guns (in Kongo), the first navy in the World to mount 16-in (406 mm) guns (in Nagato), and the first and only Navy ever to mount 18.1-in (460 mm) guns (in the Yamato-class). The Yamato class were the largest, heaviest, and most powerful battleships ever constructed.

In 1928, she launched the innovative Fubuki-class destroyer, introducing enclosed dual 5-inch turrets capable of anti-aircraft fire. The new destroyer design was soon emulated by other navies. The Fubukis also featured the first torpedo tubes enclosed in splinterproof turrets.

Japan developed the 24-inch (610 mm) oxygen fuelled Type 93 torpedo, generally recognized as the best torpedo in the world, to the end of World War II.

As a result, the 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).

At the opening of the Pacific War in 1941, the Japanese Combined Fleet comprised 10 battleships; 10 aircraft carriers; 38 cruisers, heavy and light; 112 destroyers; 65 submarines; and numerous auxiliary warships of lesser size. Carriers would roam the Pacific with near impunity, destroying their opponents at will.

But Japan failed to effectively harness its national resources for a war with the United States. Instead its army remained committed to a conflict in China, while its navy became increasingly enamored of an advance into Southeast Asia. In planning such a campaign, the naval leadership fell prey to circular reasoning. In the climate of worsening Japanese-American relations during the late 1930s, the Imperial Navy expected Washington to reduce or eliminate oil exports. Since the United States was its major petroleum supplier, Tokyo would be obliged to look to the Netherlands East Indies. But conquering the oil fields of the Indies would embroil Japan in a conflict with Washington that it could not win without access to those oil fields.

Japan developed the concept of “Kantai Kessen” (decisive fleet battle). Kantai Kessen assumed that any war with the United States would be primarily a naval war. Therefore, Japan wanted the fight to be near the Japanese home islands. Japanese naval planning had called for the destruction of American naval strength in a climactic gun duel between battleships - a belief firmly embraced by the other major navies of the day. As technological advances increased the operating range of submarines and aircraft, the operational theater for the interception-attrition operations and the decisive battle had moved eastward, further from Japanese home waters.Throughout the 1920s the Japanese expected the decisive battle to occur near the Ryukyu Islands. By 1940 the Japanese were planning for the decisive battle to be fought in the Marshall Islands.

Japan’s traditional defensive strategy was to keep the Combined Fleet in home waters, waiting to attack the US Pacific Fleet as it sailed into the Western Pacific to liberate the Philippines. The Pacific Fleet had to be destroyed in a decisive fleet engagement to force the Americans to negotiate for peace with Japan. But Japan lacked the industrial base to support a long war against the United States. If Japan did not win in 1942 the United States would build up sufficient military strength for a powerful counterattack beginning in 1943.

The desire for a quick, decisive victory led Tokyo to neglect unglamorous but vital dimensions of operations such as logistics and personnel policy. Because its leadership assumed that a war with America would be decided by a few decisive battles, the Japanese ignored such capabilities as commerce protection and antisubmarine warfare, deficiencies which became crippling vulnerabilities in a long war of attrition.

Due to the distances involved, logistics was critical to Japan. Japan maintained its ports and navy yards throughout the home islands. They maintained larger bases at locations, including Yokosuka, Kure, Sasebo, Maizuru, and Bako. These bases could provide all required services for ships up to and including overhaul. There were many smaller yards and bases throughout the home islands that provided more limited support. Japan, like the United States, depended on forward bases for their ships. Their base on Truk Island was the most advanced, with services including refuel, rearming, and repairing. Other bases away from the home islands were Saigon and Formosa. Like the United States, Japan’s ships could also refuel while under way, but it was not a practiced skill and was very rarely used. The Japanese navy had built a lot of ships, but it, like the United States, did not have enough logistics ships to properly support its fleets.

The attrition rate of Japanese destroyers was extremely high due to the need to use them for transporting supplies to the many scattered island garrisons.



The Battle of Coral Sea (7–8 May 1942) was the first “Carrier vs. Carrier” battle, and the first of the Pacific War’s six fights between opposing aircraft carrier forces. Japan lost the light Carrier SHOHO, the large Carrier SHOKAKU was heavily damaged, and the ZUIKAKU air wing was heavily damaged. The LEXINGTON was lost to spreading fires, and YORKTOWN was damaged by bombs and returned to Pearl Harbor for repairs.

The Battle of Midway, 4-7 June 1942, represented the strategic high water mark of Japan's Pacific War. Prior to this action, Japan possessed general naval superiority over the United States and could usually choose where and when to attack. Midway cost Japan four irreplaceable fleet carriers, while only one of the three US carriers present was lost. After Midway, the two opposing fleets were essentially equals, and the United States soon took the offensive. On 7 August 1942, the first US land offensive of WWII commenced, with the US Marines landing on Guadalcanal and Tulagi, Solomon Islands. Japanese victory was impossible by late 1942, but the Japanese leadership continued fighting for another three years.

From the time of the naval battles around Gudalcanal in November 1942 until the Marianas campaign in June 1944, there were no fleet to fleet engagements of consequence. The Leyte (Philippines) landings on 20 October 1944 brought on the desperate, almost suicidal, last great sortie of the Imperial Japanese Navy. Its plan for the Battle for Leyte Gulf included a feint by a northern force of planeless heavy attack carriers to draw away the American warships protecting the landings. On 24 October 1944 planes from American carriers sank four of the Japanese carriers.

By 1945, Japan was at war with more than fifty nations -- more than half the world.



The Japanese Navy was a pioneer in naval aviation, having commisioned the world's first built-from-the-keel-up carrier, the Hosho. Throughout the 1920's and 1930's, they constantly experimented with their carriers, perfecting their design and construction methods, and honing the demanding art of blue-water power projection. They also put in place a tremendously selective and rigorous pilot training program. As a result, by the time Japan attacked the United States, they possessed a fantastically effective naval aviation force, comprised of a core of six large carriers and several more light carriers, whose airwings were manned by long-serving, highly-skilled pilots. For the first six months of the war, this force would roam the Pacific with near impunity, destroying their opponents almost at will. And even well after the debacle at Midway, Japanese carriers and their airwings retained a formaidable punch.

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.

Prior to World War II several navies operated aircraft carriers or aircraft support ships. The three major powers, England, the USA, and Japan developed what came to be known as fleet carriers and gave much thought as to their most effective employment. From a glance at the ship listings it might seem that the aircraft carrier was the dominant force but this was not so. The "gun club" element still dominated strategic thought in all three navies. Carriers were regarded as supporting ships to the battle line, providing scouting planes to locate the enemy and to launch strikes to "soften up" the opposing fleet so they could be finished off by the battleships. Nowhere was the cult of the battleship as "queen of battle" more strongly entrenched than in the Imperial Japanese Navy. Their strategic plan for fighting the US Navy was to lure the American fleet across the Pacific for a great climactic battle in home waters. The total destruction of this invading force was to be accomplished by... the battleships, much as the Russian fleet was annihilated at the Battle of Tsushima. That the battleship was still predominant in IJN planning is supported by their commitment to the construction of the most powerful examples of the type ever built, the Yamato class. With the formation of the Kido Butai, (the Nagumo task force), the Japanese invented the carrier task force concept that proved so effective later in the war. Obviously there were many officers with advanced ideas regarding carrier aviation but they were still in the minority. In the IJN the "gun club" still controlled planning and policy decisions.

Ironically, the Japanese Navy was to prove the fallacy of this thinking with their preemptive strike on the USN battle line at Pearl Harbor. With no battleships available the USN was forced to shift their emphasis to the aircraft carrier as the center of a striking force, though they still continued to build a new generation of battleships. At the Battle of the Coral Sea neither fleet sighted the other, the entire battle being decided by carrier aircraft. At Midway, when four Japanese carriers were lost orders were issued to continue the operation. The battle fleet was to close and destroy the American ships. After a few hours of steaming towards Midway the orders were rescinded and the surface fleet withdrew. The lesson was obvious and could not be ignored. A surface fleet could not survive without carriers when facing a fleet that had them. The battleships were impotent in the face of this new threat.

In the days following the debacle at Midway, the Japanese Navy frantically sought ways to make good their carrier losses. Some submarine tenders and seaplane tenders were available for conversion to carriers, (they had been designed with this in mind). Suitable commercial liner hulls were taken over for conversion to light carriers. Most radical, especially in the eyes of traditional line officers, was the plan to take four battleships out of the battle line and modify them to operate aircraft. The Fuso, Yamashiro, Ise, and Hyuga were selected for this conversion which consisted of removing the aft two turrets and constructing a handling deck, hangers and two catapults. The decks would not be large enough for take off or for landing aboard so the aircraft would have to be catapult launched and be equipped with floats to land alongside and be hoisted aboard. A new type of fast seaplane, capable of both scouting and attack, was to be designed for these ships. Conversion began on the Ise and Hyuga but the planned work on Fuso and Yamashiro was held back pending testing results from the first two ships. Work on the seaplane, the "Norm", went forward but very few were built. Neither Ise or Hyuga ever operated aircraft apart from some limited testing. There were never enough aircraft to equip the ships and there was also a shortage of trained pilots. In their only sortie in this configuration, the Battle of Leyte Gulf, both ships were part of the Ozawa decoy force and had no aircraft on board. Almost all of the carriers in this group were sunk but both Ise and Hyuga sustained only minor damage.



The Imperial Japanese Navy entered the Second World War with a state-of-the-art fleet of warships. By the end of the war, a majority of these ships, estimated to be about 2,500 vessels, were sunk, or made inoperable due to damage. Although Japanese warships were some of the most graceful warships built, photographic records and technical details of these ships are relatively scarce since a significant portion of this material was lost during the war. Many were beautiful and unique ships with the long sweeping hulls characteristic of Japanese warships.

Japanese destroyers, starting with the Fubuki class, began the state of the art destroyer design for World War II. With enclosed, double turrets and heavy gun and torpedo armament, the Fubuki's and their successors, the "special type," set the standard for all later design -- although the Japanese desire to pack as much as possible onto the ships tended to make them top heavy. With the design also went the tactics.

As the means of protecting capital ships from torpedo boats, the kind of ship originally called the "torpedo boat destroyer" eventually, with Japanese tactics (first in the Russo-Japanese War, 1904-1905), came into its own as the successor to the torpedo boats. The Imperial Japanese Navy (IJN, Nihon Teikoku Kaigun, ) had excellent torpedoes, and they planned how to use them. Japanese torpedoes had very long ranges; but the best shot for torpedoes is always as close as possible, and the best circumstances for close shots are at night. The Japanese navy thus drilled and planned for night combat. Only the British Royal Navy had a similar emphasis, after their mortifying experience of the Germans escaping in the night at the battle of Jutland in 1916.

The Royal Navy would use its night training to devastate the Italian navy at the battle of Matapan in 1941, but then the Japanese would frequently use their night training to devastate both the British and United States navies in 1941, 1942, and 1943. The campaigns in Indonesia, culminating in the battle of the Java Sea, 27 February 1942, and then the long campaign in the Solomon Islands from 1942 to 1943, provided many opportunities for Japanese torpedo and night combat training to pay off. On the other hand, the United States Navy was dominated by a group, derisively called the "Gun Club," that emphasized tactics based on gunnery. American torpedoes, poor in themselves, were actually removed from cruisers. There would be hell to pay for this bias.

The supreme achievements of Japanese torpedo and night combat were the battles near Guadalcanal of Savo Island, 9 August 1942, and Tassafaronga, 30 November 1942. The Savo Island force, ironically, consisted entirely of cruisers, except for a single pre-Fubuki destroyer, the Yunagi, trailing along. But the destroyers would get their chance. Indeed, as attrition mounted off Guadalcanal, and then the battleships Hiei and Kirishima were sunk there in the Naval Battle of Guadalcanal, 12-15 November 1942, Japan gave up seriously contesting the waters, and used destroyers for such actions as were necessary -- combat and both to supply the troops on Guadalcanal and then finally to take them off.

In the course of one such operation, a very superior American force surprised Japanese destroyers in the battle of Tassafaronga. Turning away and filling the water with torpedoes, the Japanese force only lost one ship, while sinking or seriously damaging several American heavy cruisers. For the time being, that all but knocked the American cruisers, like the Japanese, out of the war; and, mercifully, it was about the end of the line for the "Gun Club." American destroyers finally came into their own with victory in the battle of Vela Gulf, 6/7 August 1943. In subsequent battles in the Solomons, the Japanese were without all of their previous advantages, and their reliance on destroyers to carry the brunt of supply as well as combat actions simply meant a terrific attrition in the destroyer force.

Besides their excellent design and combat history, perhaps the most striking thing about Japanese destroyers are their names. They were named after phenomena of weather, sea, and sky, with several groups based on wind, snow, rain, clouds, waves, mist, frost, tides, and moons. In compounds, the unvoiced initial consonants of these are often voiced, e.g. gumo for kumo or zuki for tsuki. Seldom have so many poetic names been bestowed on such devices of violence, although characteristic of the Japanese moral aestheticism that made war and death things of art and beauty.

It is no accident that destroyers were frequently named in groups of four, e.g. four "-gumos" or "-shimos." Such groups of four ships would then later operate as single destroyer squadrons. Several squadrons would then be collected into a destroyer flotilla commanded by a Rear Admiral, who would fly his flag in one of the older cruisers.Such cruisers were so lightly armed that by World War II they were little better than large destroyers, which is how they were used -- the equivalent of what would have been called a "destroyer leader" elsewhere.

The "London Treaty" refers to the London Naval Treaty of 1930, under whose limitations two classes of ships were built. The subsequent "cruiser" types, like the Yugomo, were built free of the limitations of naval treaties, which had been repudiated. They therefore represent the most advanced thinking of the Japanese naval architects. The final "anti-aircraft" class of large destroyers is the only attempt made in this direction comparable to the American anti-aircraft light cruisers, like the Atlanta and Juneau (both tragically sunk when improperly deployed into surface combat around Guadalcanal).

The term "Treaty Cruisers" refers to the cruisers built under the treaty restrictions of the Washington Naval Treaty of 1921 and the London Naval Treaty of 1930. In both treaties the maximum tonnage for cruisers was set at 10,000 tons. The maximum size gun for a cruiser under the Washington Treaty was 8 inches and under the London Treaty 6 inches.

Since the Japanese, especially, felt unfairly limited by the Washington Treaty, they immediately began planning ships right up to the treaty limits. Not only that, but they began designing them like little battleships, with enclosed turrets, but still with torpedoes, ready for close action surface fights, especially at night. Their first ships mounted six guns, but after four of those, they began mounting ten guns, which became the standard outfit for Japanese heavy cruisers.

Note that Japanese heavy cruisers, like battlecruisers, are named after mountains. Thus, if the name is found on a map of Japan, it will be followed by the character , which in Japanese will be pronounced yama, san, or zan. Light cruisers are named after rivers, for which the character will be , pronounced kawa or gawa. The very last Japanese cruiser should be be named after a river, which could be the Sakawa, containing "river" as part of the name; but the actual name of the ship is written , with a final character that doesn't exist in Chinese, and is read nioi in Japanese. How that character comes to be read "kawa" or "wa" is a good question, although things like this are not unusual in Japanese. The first character can be read "shu" or "sake" -- the name appears to mean the "fragrance of sake." Although the Mogami class were refitted as heavy cruisers, they retained the river names of light cruisers (e.g. named after the Mogamigawa). Similarly, although the Tone class were completed as heavy cruisers, they had been ordered as light cruisers and also retained the river names of light cruisers (e.g. named after the Tonegawa).

There are several landmarks in the history of building a ship. A ship is (1) ordered, (2) laid down, (3) launched, (4) completed, and (5) commissioned. "Laid down" means, of course, that construction is started. When the hull is complete enough for the ship to float, it is launched. Much of the construction of a ship is thus subsequent to launching. Once the ship is completed, it can be tested at sea. Not until the tests are completed is a ship "commissioned," which means it is accepted into active service, with a crew and commanding officer. A commissioned ship has a watch on duty at all times, in port or at sea. A ship that is laid up in reserve, with no crew, has been "decommissioned."

Britain and the United States soon responded in kind to the Japanese. The British never mounted more than eight guns in their main batteries. They were much more concerned about numbers of ships than the Japanese, since they had three oceans to worry about and several major dependencies, Canada, India, South Africa, Australia, and New Zealand, for whom Britain was still largely responsible for defense. Thus, after several cruisers with eight guns, newer ones with only six were built. The United States at first responded with ten guns, like the Japanese, but then settled into nine guns in three triple turrets, which became standard thereafter. Since the United States did not have the international defense commitments of Britain in the 1920's, the American response to Japan was more leisurely; and the American ships, although ordered in a timely fashion, were completed rather slowly. Thus, although the first American Treaty Cruiser was not launched until 1929, the ships were ordered and designed several years earlier.

More troubling than this delay was one feature of American doctrine. The new cruisers were left without torpedo tubes. This was the effect of what was called the "gun club" in the U.S. Navy, the dominant group who thought that long range gunfire would dominate naval actions. This did not take into consideration the conditions of night combat. Or the fact that aircraft, not guns, would dominate day battles. Ship to ship actions in World War II would tend to be at night. Darkness and uncertainty would put a premium on tactics for close action, and torpedoes could be decisive in those circumstances. The Japanese and British devoted considerable effort to night training (though the British don't seem to have been aware of the Japanese training, even though it had been Japanese doctrine since 1904), and the Japanese also devoted considerable effort to developing first rate torpedoes. American torpedoes, on the other hand, were riddled with defects which insufficient testing did not uncover until long after the War had started. This was especially bad for American submarines, many of which may have been lost because of dud torpedoes -- for a long time the Bureau of Ordinance (BuOrd) simply didn't believe the complaints of the submarine commanders.

The London Naval Treaty of 1930 imposed the 6 inch gun limit on new cruisers, without altering the maximum tonnage. This introduced the distinction between a "heavy cruiser" (CA), with 8 in guns, and a "light cruiser" (CL), with 6 inch guns. The American abbreviation for "heavy cruiser," CA, seems to be derived from the "armored cruisers" of the turn of the century, which is revealing, since American armored cruisers were named like battleships -- this puts the "heavy cruisers" in a branch of the battleship tradition, as they should be, since, in effect, the Treaty Cruisers replaced the pre-World War I Dreadnought race.

Again, the Japanese designed ships right up to the treaty limits, mounting 15 six inch guns on the 10,000 ton Mogami's. The American Brooklyn class matched this, but the British decided not to go along. The Japanese ships, however, would not remain "light" cruisers. Once Japan decided not to renew the London Treaty, plans were immediately begun to replace the triple 6 inch turrets on the Mogami's with double 8 inch turrets. This converted the ships into heavy cruisers comparable to the earlier Myoko's and Atago's. A small class of "light cruisers" like the British ones was also designed, but these ships were finished, during the war, too late to participate in the early battles.

In the early days of the Pacific War the United States Navy paid dear for its deficiences in doctrine and armament. The Battle of Savo Island, a brilliant surprise attack in the dead of night by Japanese Admiral Mikawa, was the worst naval defeat in U.S. history. Three American cruisers were sunk, along with the Canberra of the Royal Australian Navy. Although the Japanese campaign on Guadalcanal headed down hill after the commitment of U.S. battleships in the Naval Battle of Guadalcanal, the Japanese continued to have the advantage in night battles in the Solomons until well into the New Georgia campaign -- the losses of cruisers helped convince the "gun club" to let the destroyer commanders practice their torpedo tactics. Increasing American air dominance, and the attrition of Japanese forces, later eliminated such surface actions, except for the desperate Japanese attack in the Battle for Leyte Gulf.

Only the United States launched and completed substantial numbers of cruisers after 1941. This was mostly too late for the Solomons campaign, but it is a good indication of the overwhelming strength exerted by America that made the last couple years of the War so one sided. Most of these ships simply screened the carrier groups that took one Japanese island after another and then punished the Japanese homeland until the surrender.


Japan had what was easily the most diverse submarine fleet of any nation in the Second World War. These included manned torpedoes, midget submarines, 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 high submerged speed, and submarines that could carry multiple bombers.

The Japanese Imperial Navy started their submarine service with the purchase of five Holland type submarines from the Electric Boat Company of the United States in 1905. Japanese submarine forces progressively built up strength and expertise, becoming by the beginning of World War II one of the most varied and powerful fleets of submarines of the world.

The Imperial Japanese Navy acquired its first submarines in 1905 from the relatively new American company, Electric Boat, although the United States Government was officially neutral during Japan's war with Russia during that time.

The ships that Electric Boat sold to Japan were Holland designs, known as Holland Type VIIs and modeled after the American Plunger-class submarines. They were shipped by freighter from Seattle, Washington in "knocked-down" kit form to Japan, and then reassembled by Arthur Leopold Busch at the Yokosuka Naval Arsenal, which was then Japan's largest naval shipyard, to become Hulls No. 1 through 5. These five submarines were originally built at Fore River Ship and Engine Company in Quincy, Massachusetts under Busch's direction for the Electric Boat Company back in August-October 1904.

Frank Taylor Cable, an electrician who was working for Isaac Rice's Electro-Dynamic and Storage Companies along with Rice's Electric Boat, arrived some six months after Busch, training the IJN in the operation of such craft.

The Kawasaki Dockyard Company also bought plans of an improved version directly from Holland, and built two ships (Hulls No. 6 and 7), with the help of two American engineers, Chase and Herbert, who had been assistants to Holland.

Although the capabilities of these first ships actually proved disappointing (and were of no help in the Russo-Japanese War), the first submarine squadron was soon formed at Kure Naval Base in the Inland Sea. In 1909, the first submarine tender, Toyorasi, was commissioned.

German submarine successes in the Northern Atlantic during the First World War further reinforced Japan's willingness to develop this weapon. Eighteen ocean-going submarines were included in the 1917 expansion program. At the end of the war, Japan also received nine German submarines as reparations, which allowed her to accelerate her technological development during the interwar period.


Japan had the most varied fleet of submarines of World War II; including manned torpedoes (Kaiten manned torpedos), midget submarines (Ko-hyoteki and Kairyu), medium-range submarines, purpose-built supply submarines and long-range fleet submarines. They also had submarines with the highest submerged speeds during world war II (Sen taka I-200 class submarines) and submarines that could carry multiple aircraft the (Sen toku I-400 class submarine). They were also equipped with the most advanced torpedo of the entire conflict, the oxygen-propelled Type 95.

The type 95 torpedo was a torpedo of the Imperial Japanese Navy. Based on the very formidable 'long lance' type 93 oxygen-driven torpedo, the Type 95 had a smaller 893-pound (405kg) warhead, less range and a smaller diameter, and intended to be fired from a standard 21-inch (533mm) torpedo tube of a submerged submarine. Its range was 9,900 yards (9,000m) at 49-50 knots, or 13,200 yards (12,000m) at 45 knots. That's about three times the range of the American Mark 14 at the same speed.

With a top speed of 49-50 knots, the Type 95 was the fastest torpedo in common use by any navy at the time. Its warhead size was the largest of any submarine torpedo, and second only to the Type 93 'Long Lance' used by Japanese surface ships. Some have claimed these to be the best torpedoes of the Second World War.

Nevertheless, despite their technical prowess, Japanese submarines were relatively unsuccessful. They were often used in offensive roles against actual warships, which were fast, maneuverable and well-defended compared to merchant ships (such as German U-boats tended to prey upon). In 1942, Japanese submarines sank two aircraft carriers among other warships, but were not able to obtain similar results afterwards. By the end of the war, submarines were instead often used to transport supplies to island garrisons.


Because of the vastness of the Pacific, Japan built many boats of extreme range and size, many of which were capable of cruises exceeding 20,000 miles and lasting more than 100 days. In fact, Japan built what were by far the largest submarines in the world, indeed, the only submarines over 5,000 tons submerged displacement, or submarines over 400 feet in length until the advent of nuclear power. These same boats were credited with a range of 37,500 miles at 14 knots, a figure never matched by any other diesel-electric submarine. These large boats could each carry three floatplane bombers, the only submarines in history so capable. Japan built 41 submarines that could carry one or more aircraft, while the vast submarine fleets of the United States, Britain, and Germany included not one submarine so capable.

During the Second World War, there were 56 submarines larger than 3,000 tons in the entire world, and 52 of these were Japanese. Japan built 65 submarines with ranges exceeding 20,000 miles at ten knots, while the Allies had no submarine capable of this feat. By 1945, Japan had built all 39 of the world's diesel-electric submarines with more than 10,000 horsepower, and all 57 of the world's diesel-electric submarines capable of 23+ knots surface speed.

The Japanese applied the concept of the "submarine aircraft carrier" extensively. Altogether 47 submarines were built with the capability to carry seaplanes. Most IJN submarine aircraft carriers could carry only one aircraft, but I-14 had hangar space for two, and the giant I-400 class three.

By design, the I-400 class had a range of 37,500 nautical miles at a cruising speed of 14 knots, all in all, a formidible weapon.

Submarine aircraft carriers are submarines equipped with fixed wing aircraft for observation or attack missions. These submarines saw their most extensive use during World War II, although their operational significance remained rather small. The most famous of them were the Japanese I-400 class submarine and the French submarine Surcouf, although a few similar craft were built by other nations' navies as well.

Early models were not very maneuverable under water, could not dive very deep, and lacked radar. (Later in the war units that were 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 equipped submarines in the span of four days).

Germany was the first nation to experiment with submarine aircraft carriers, inspired by the Imperial German Naval Air Service commander Oberleutnant zur See Friedrich von Arnauld de la Perriére. He commanded a unit of two reconnaissance seaplanes (Friedrichshafen FF.29s) in Zeebrugge which had been recently occupied by the Imperial German Army in the early months of World War I. One of the first U-Boats to arrive at the Zeebrugge base was Kapitanleutnant Walther Forstmann's U-12, which was to play the role of submarine aircraft carrier.

The Sen Toku I-400-class submarines of the Imperial Japanese Navy were the largest submarines of World War II, and the largest ever built prior to the development of nuclear ballistic missile submarines in the 1960s. They were submarine aircraft carriers able to carry 3 Aichi M6A Seiran aircraft underwater to their destinations. They were designed to surface, launch the planes then dive again quickly before they were discovered. They also carried torpedoes for close range combat.

The I-400 class was designed with the range to travel anywhere in the world and return. A fleet of 18 boats was planned in 1942, and work started on the first in January 1943 at the Kure, Hiroshima arsenal. Within a year the plan was scaled back to five, of which only three (I-400 at Kure, and I-401 and I-402 at Sasebo) were completed.

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 US Navy in 1946 when the Soviets demanded to have access to the advanced submarines as well.

Until the advent of the American and Russian nuclear "super-subs" of the late 1950's and '60's the I-400 seriesl had reigned as the biggest submarine ever built. And she was not alone ... of some seventeen planned, three were actually completed and built.

Were they a ridiculous, pointless weapon ... of little significance, but of great curiosity ? ... or were they a formidable strategic naval weapon ... ahead of their time ?

After much research and study (... these boats absolutely fascinate me!) I have come to the frightening conclusion that they were in fact, the latter. And I use the word "frightening" advisedly!

Notwithstanding the commonly known fact that they were intended to be used to attack and disable the locks of the Panama Canal (a perfectly logical target ... and an action that may have had a severe impact upon the allied war effort), the original concept and construction of these gigantic boats would also appear to have been connected with contemporary Japanese nuclear research, and the ties established with Nazi Germany regarding similar research. These ties had resulted in (limited) sharing of information and reciprocal transference of knowledge and materials in thisregard. Research and development of bacteriological weapons was also in consideration .. and under way.

Gets scary .... doesn't it?!

The truth is .... the I-400 boats were originally conceived to attack Los Angeles, San Francisco, New York, Philadelphia and Washington D.C ... probably with "dirty" nuclear, or bacteriological weapons! .....and, had the timing been right ... they could have done it!

They were formidable boats. With a range of better than 30,000 miles(!) each boat carried three Aichi "Seiran" bombers (plus a disassembled fourth). The "Seiran" wasn't a small reconnaissance aircraft - but a fully fledged torpedo-bomber developed from the well proven Yokosuka D4Y "Suisei" (Allied code-name)"Judy" that had demonstrated its effectiveness throughout the previous few years as a credible combat aircraft. Three of these boats would have been capable of (and at one time were intended to be used for ...) launching a squadron of these puppies ... over New York!

It might not have won the war for Japan. But it would have been a most terrifying chapter to have added to an already terrifying story ...... had it happened!

As it was, the three I-400 class submarines were dispatched to attack the U.S. fleet in Ulithi Atoll in late 1945 ... only to be recalled to surrender before they saw action. I-400 and I-401 eventually landed in Pearl Harbor - were exhaustively examined and scuttled. I-402 was eventually scuttled off Kure in Japan by U.S. forces and lies there to this day.

Indeed ... strategic weapons ... well ahead of their time ... and ... (thankfully) ... never used ...

So we move forward almost 59 years to the 17th. of March 2005, and the wreck located off Oahu by the team from the University of Hawaii is that of U-401.

On Sunday the 20th. of March 2005 details of a research team from the University of Hawaii finding the wreck of WW2 Japanese Submarine I-401 were released. On St Patrick's day, the 17th.of March, during test dives off Oahu, a wreck was found - to quote the pilot of the research vessel Terry Kirby: " We thought it was rocks at first, it was so huge, but the sides of it went up, and up, and up, three or four stories tall. It is a levithian down there, a monster." Kirby went on to say, the main hull is in good shape, the numbers I-401, clearly visible on the sides, and her AA guns in almost perfect condition.

Now, much excitement that one of that number has been discovered again, but, what will now result remains to be seen.

The deep ocean floor may for years hold her secrets closely, but modern underwater vehicles, improved technical sound equipment, operated with patience, and sufficient research funds, will ultimately prize open these secrets, and one more ship wreck comes into the public domain.


The Japanese navy also built submarines with the fastest underwater speeds of any nation's combat submarines. They employed 78 midget submarines capable of 18.5 to 19 knots submerged, and built 110 others capable of 16 knots. As the war was ending they completed four medium-sized submarines capable of 19 knots submerged. This exceeds the 17.5-knot performance of the famed German Type XXI coming into service at the same time. As early as 1938, Japan completed the experimental Submarine Number 71, capable of more than 21 knots submerged.

Japanese submarines employed the best torpedoes available during the Second World War. The Type 95 torpedo used pure oxygen to burn kerosene, instead of the compressed air and alcohol used in other nation's torpedoes. This gave them about three times the range of their Allied counterparts, and also reduced their wake, making them harder to notice and avoid. The Type 95 also had by far the largest warhead of any submarine torpedo, initially 893 pounds (405 kg), increased to 1210 pounds (550 kg) late in the war. All Japanese torpedoes made during the war used Japanese Type 97 explosive, a mixture of 60% TNT and 40% hexanitrodiphenylamine. Most importantly, the Type 95 used a simple contact exploder, and was therefore far more reliable than its American counterpart, the Mark 14, until the latter was improved in late-1943. Japan also developed and used an electric torpedo, the Type 92. This weapon had modest performance compared to the Type 95, but emitted no exhaust and, therefore, left no wake to reveal its presence. Similar electric torpedoes were used by several nations.

Given their size, range, speed, and outstanding torpedoes, Japanese submarines achieved surprisingly little. This was because they were mainly employed against warships, which were fast, maneuverable, and well-defended when compared to merchant ships. Japanese naval doctrine was built around the concept of fighting a single decisive battle, as they had done at Tsushima 40 years earlier. They thought of their submarines as scouts, whose main role was to locate, shadow, and attack Allied naval task forces. This approach gave a significant return in 1942 when they sank two fleet carriers, one cruiser, and a few destroyers and other warships, and also damaged two battleships, one fleet carrier (twice), and a cruiser. However, as Allied intelligence, technologies, methods, and numbers improved, the Japanese submarines were never again able to achieve this frequency of success. For this reason, many argue that the Japanese submarine force would have been better used against merchant ships, patrolling Allied shipping lanes instead of lurking outside naval bases. Bagnasco credits the Japanese submarine fleet with sinking 184 merchant ships of 907,000 GRT. This figure is far less than achieved by the Germans (2,840 ships of 14.3 million GRT), the Americans (1,079 ships of 4.65 million tons), and the British (493 ships of 1.52 million tons). It seems reasonable that an all-out blitz of the American west coast, the Panama Canal, and the approaches to Hawaii, New Zealand, Australia and India would have caused the Allies more difficulty than did the naval deprivations that were actually achieved. Losing a significant number of merchant ships, and also needing to spread meager defenses even more thinly along two coasts, would surely have had some substantial consequences for the United States in 1942.

Imperial Japanese Navy submarines formed 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 Imperial Japanese Army), fleet submarines (many of which carried an aircraft), submarines with the highest submerged speeds of the conflict (Sentaka I-200), and submarines able to carry multiple bombers (WWII's largest submarine, the Sentoku I-400). They were also equipped with the most advanced torpedo of the conflict, the oxygen-fuelled Type 95. A plane from one such fleet submarine, I-25, conducted what is still the only 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. In February 1942 the submarine I-17 launched a number of artillery shells at the Elwood Oil Fields near Santa Barbara, California. None of the shells caused any damage.

Overall, despite their technical innovation, Japanese submarines were built in small numbers and had less effect on the war than those of the other major navies. Due to IJN's adherence to a flawed Mahanian doctrine, they were often used in offensive roles against warships, 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. However, these were aided by the limited resources of the US Navy at the time. Once the US was able to ramp up construction of destroyers and destroyer escorts, as well as bringing over highly effective anti-submarine techniques learned from the British from experiences in the Battle of the Atlantic, they would take a significant toll on Japanese submarines, which tended to be slower and could not dive as deep as their German counterparts. Japanese submarines, in particular, never menaced the Allied merchant convoys and strategic shipping lanes to the degree that German U-boats did.

The Japanese did, of course, make some attacks on merchant shipping in the Pacific and Indian Oceans, but these were the minority of missions. Frequently, they waited for fleets that were never seen, supported spectacularly brave but inconsequential reconnaissance flights, or toted midget submarines about, all of which achieved rather less than was possible with so valuable a resource as the Japanese submarine fleet. Worse from a naval perspective, Japanese submarines were increasingly employed in running supplies to the starving garrisons of isolated islands. The Japanese expended hundreds of sorties in this way, which might have otherwise been used offensively against the Allied war effort. A submarine's cargo capacity was much less than that of a relatively inexpensive freighter. However, Japan was understandably reluctant to let island garrisons starve. Additionally, many practically unarmed submarines (including 26 built for Army use) were built specifically for the supply role, consuming production resources as well.

For their disappointing achievements, Japanese submarines paid heavily. Japan started the war with 63 ocean-going submarines (i.e., not including midgets), and completed 111 during the war, for a total of 174. However, three-quarters of these (128 boats) were lost during the conflict, a proportion of loss similar that experienced by Germany's U-Boats. Most of the surviving boats were either dedicated to training roles or were recently completed and never saw combat. Of those which saw significant combat, the toll was very grim indeed. For example, of the 30 submarines that supported the Pearl Harbor attack, none survived the war.

Compared to German submarines, Japan's huge boats were relatively easy to sight visually and with radar, slow to dive, hard to maneuver underwater, easy to track on sonar, and easy to hit. Japanese hulls were also not as strong as those of German boats, and therefore could not dive as deeply nor survive such rough treatment. Also, they lacked radar until the first sets were installed in June 1944, and never had sets as good as the Allies possessed.

Advances in convoy tactics, high frequency direction finding (referred to as "Huff-Duff"), radar, active sonar (called ASDIC in Britain), depth charges, ASW spigot mortars (also known as "hedgehog"), the introduction of the Leigh Light, the range of escort aircraft (especially with the use of escort carriers), and the full entry of the U.S. into the war with its enormous shipbuilding capacity, all turned the tide against the submarine.

Compounding these deficiencies, Japan was at war with the United States and the United Kingdom, two nations embroiled in a vast conflict with hundreds of U-Boats in the Atlantic, and hence two nations which poured lavish resources into anti-submarine warfare (ASW) research and development. As an example of the fruits of this research, in June 1944 the US Navy sank the I-52 by using code-breaking to discover her schedule, finding her at night with radar-equipped carrier-based aircraft, tracking her underwater with sonobuoys dropped by those aircraft, and sinking her with acoustic homing torpedoes dropped by the same aircraft. The Japanese could achieve none of these technological feats at that time.

In the face of such disadvantages, morale declined within the Japanese submarine force. This is reflected in a post-war report prepared by the US and British Navies which states, "It was frankly impossible to believe that submarines could spend weeks on the US west coast 'without contacts,' or spend more than 40 days running among the Solomons during the Guadalcanal campaign 'without seeing any targets.' Even the Japanese commanding officers could not disguise their embarrassment when recounting these tales. Further enlightenment is found in the extremely large number of times the target was 'too far away to attack.'"

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 Great Britain (493 ships), 5.2 million tons for the U.S. (1314 ships),and 14.3 million tons for Germany (2,840 ships).


Between 1943 and 1945, a group of U-boats known as the "Monsun Boats" (Monsun Gruppe) operated in the Indian Ocean from Japanese bases in occupied Indonesia. As the Allied merchant convoys had not yet been organized in those waters, the initial sinkings were plentiful. However, this situation was soon remedied. During the later war years, the "Monsun Boats" were also used as a means of exchanging vital war supplies with Japan.

The Monsun Gruppe (or Monsoon Group) was a force of German U-boats (submarines) that operated in the Pacific and Indian Oceans during World War II.

The Indian Ocean was considered strategically important, the region not only contained India, Britain's most prized possession, but also the shipping routes and raw materials that the British vitally needed for its war effort. In the early years of the war German raiders and capital ships, operating in the Indian Ocean, had sunk a number of merchant ships, however as the war progressed it become more difficult for them to operate in the area and by 1942 most were either sunk or dispersed. From 1941, U-boats were also considered for deployment to this area but due to the successful periods known as the First and Second Happy Times, it was decided that sending U-boats to the Indian Ocean would be an unnecessary diversion. There were also no foreign bases in which units could operate from and be resupplied, hence they would be operating at the limits of their range. As a result the Germans concentrated their U-boat campaign in the North Atlantic.

Japan’s entrance into the war in 1941/42 led to the capture of European South-east Asian colonies such as British Malaya and the Dutch East Indies. In May-June, 1942, Japanese submarines began operating in the Indian Ocean and had engaged British forces in Madagascar. The British had invaded the Vichy controlled island in order to prevent it from falling into Japanese hands.

In 1943, the Germans agreed to send a number of U-boats to the Far East that would operate from Japanese occupied ports in the region against the then lucrative, relatively unprotected shipping in the area. The U-178 was the first, arriving at the former British seaplane base in Penang in August 1943. The idea of stationing U-boats in Malaya and the East Indies for operations in the Indian Ocean was first proposed by the Japanese in December 1942. As no supplies were available at either location the idea was turned down although a number of U-boats from the first wave operated around the Cape of Good Hope at the time. Penang, situated on the west coast of Malayan Peninsula was selected as the main U-boat base. A second base was established at Kobe, Japan, and small repair bases were located at Singapore, Jakarta and Surabaya. Eventually more than half a dozen U-boats operated from these bases. These U-boats were known as the "Monsun Gruppe" and were commanded by Captain Wilhelm Dommes. Altogether 41 U-boats of all types including transports would be sent, a large number of these however, were lost and only a small fraction returned to Europe.

The Italian Royal Navy (Regia Marina) converted four submaries into "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. They converted the Barbarigo, the Cappellini, the Giuliani, and the Torelli. After Italy quit the war in 1943, the Cappellini was taken over by the German Navy (Kriegsmarine) and re-named the UIT-24. When Germany surrendered in 1945, the UIT-24 was taken over bt the Imperial Japanese Navy and re-named the I-503. The Torelli shared a similar story.

The Japanese already started operating in the Arabian Sea by August 1943 and certain arrangements were made to avoid incidents between U-boats and Japanese submarines - attacks on other submarines were strictly forbidden. The Indian Ocean was the only place where German and Japanese forces fought in the same theatre.

The idea of stationing German U-boats in Penang or Sabang for operations in the Indian Ocean was first proposed by the Japanese in December 1942. As no supplies were available at either location the idea was turned down (although a number of U-cruisers from the first wave operated around the Cape at the time).

The idea was raised again in the spring 1943. Additionally, the Japanese requested 2 U-boats to be handed over for copying. Although Doenitz saw no point in such a handover, it was decided to give a type IXC boat.

As long as targets were available in the Atlantic, Doenitz considered sending U-boats on a large scale to the Far East as unprofitable. However, on 5 April, 1943 it was decided to send U-178 to Penang to establish the naval base there. U-511 sailed soon after to be eventually given to the Japanese in return for rubber.

It is also reported that U-511 arrived at Penang around 17 July, 1943 as the first German U-boat to enter the base (before U-178).

U-511 scored some success while on the passage to Japan. The boat carried Vice-Admiral Nomura (the Japanese Naval Attache) and in September 1943 was recommissioned as RO-500. U-511's crew was to be a spare crew for the boats which were later to operate from the Japanese-held bases.

After the May 1943 crisis it was decided to look for less strongly defended areas and the idea of sending boats to the Far East was finally approved. Indian Ocean was the only region with almost peace-time shipping arrangement and still with U-boats radius of action.

As the result arrangements were made to replenish U-cruisers still operating around the Cape and to send a new wave of boats for the attack in the Arabian Sea. The latter was scheduled for the end of September 1943 - right after the monsoon period. Because of this the group was named Monsun. The group was to sail in June 1943 at the latest.

Very few patrols with the intention to return back to the Far East bases were attempted by the Monsun boats.

One of the reasons for disappointing results was the quality and quantity of torpedoes available at Penang. They were derived from German armed merchant cruisers and blockade-runners and suffered badly from the long storage in the tropics. To make up for this special torpedo transports of type VIIF were sent with torpedoes and spares. Also further operational boats were systematically sent to the Far East:

It can be seen that the effort was gradually shifted from combat missions to transport missions. Some of the boats were even permanently converted to transports. How important the transport missions were can be judged from the fact that even in the spring 1945 U-boats were still sailing to the Far East. Some of them with interesting cargoes indeed - like well-known U-234. U-874 and U-875 were loading some 170 tons of mercury, lead and optical glass but never managed to leave European waters.



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NB: The above text has been collected / excerpted / edited / mangled / tangled / re-compiled / etc ... from the following online sources :

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