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The Imperial Japanese Navy (大日本帝国海軍) built four battlecruisers, with plans for an additional four, during the first decades of the 20th century. The battlecruiser was an outgrowth of the armoured cruiser concept, which had proved highly successful against the Russian Baltic Fleet in the Battle of Tsushima at the end of the Russo-Japanese War. In the aftermath, the Japanese immediately turned their focus to the two remaining rivals for imperial dominance in the Pacific Ocean: Britain and the United States. Japanese naval planners calculated that in any conflict with the U.S. Navy, Japan would need a fleet at least 70 percent as strong as the United States' in order to emerge victorious. To that end, the concept of the Eight-Eight fleet was developed, where eight battleships and eight armoured cruisers (by that time, they would inevitably become battlecruisers) would form a cohesive battle line. Similar to the German Imperial Navy (Kaiserliche Marine) and in contrast to the Royal Navy, the Japanese envisioned and designed battlecruisers that could operate alongside more heavily armoured battleships to counter numerical superiority.

The first phase of the Eight-Eight plan began in 1910, when the Diet of Japan authorised the construction of one battleship (JAPANESE BATTLESHIP Fusō) and four battlecruisers of the Kongō-class battlecruiser. Designed by British naval architect George Thurston, the first of these battlecruisers (JAPANESE BATTLESHIP Kongō) was constructed in Britain by Vickers, while the remaining three were constructed in Japan. Armed with eight 14 in guns and with a top speed of 30 kn, they were the most advanced capital ships of their time. The first battlecruisers to enter service in the Imperial Japanese Navy though, were the Tsukuba-class cruiser and Ibuki-class battlecruiser in August 1912. Both were originally built and commissioned as armoured cruisers, then were reclassified as battlecruisers. Although the two Tsukuba and two Ibuki class ships possessed battleship-grade 12 in guns, their lack of uniform gun layout made them inferior to true "all big gun" battlecruisers, and were not included in the Eight-Eight plan. At the height of the First World War, an additional four battlecruisers of the Amagi-class battlecruiser were ordered. The ships would have had a main battery of ten 16 in guns, but none were ever completed as battlecruisers, as the Washington Naval Treaty limited the size of the navies of Japan, Britain and the United States. Before the Second World War, a further class of two battlecruisers were planned (Design B-65), but more pressing naval priorities and a faltering war effort ensured these ships never reached the construction phase.

Of the twelve battlecruiser hulls laid down by Japan (the two Tsukuba, two Ibuki, four Kongō and four Amagi class), none survived the Second World War. Tsukuba was destroyed 14 January 1917 while in port at Yokosuka when a fire in her ammunition magazine caused a massive explosion, killing 305 men. Amagi was being converted to an aircraft carrier when its hull was catastrophically damaged by the Great Kantō earthquake in 1923 and subsequently broken up, while the last two of the Amagi class were scrapped in 1924 according to the terms of the Washington Treaty, along with the JAPANESE CRUISER Ikoma, JAPANESE BATTLESHIP Ibuki and JAPANESE BATTLESHIP Kurama a year earlier, in 1923. JAPANESE AIRCRAFT CARRIER Akagi was converted to an aircraft carrier in the 1920s, but was scuttled after suffering severe damage from air attacks during the Battle of Midway on 5 June 1942. The four Kongō-class ships were lost in action as well: two during the Naval Battle of Guadalcanal in November 1942, one by American submarine in November 1944, and one by American aircraft at Kure Naval Base in July 1945.

Ibuki class


The two Ibuki-class battlecruiser were originally ordered during the Russo-Japanese war in 1905 as a new class of armoured cruisers, with heavy battleship-grade guns, capable of overpowering existing armoured cruisers and were intended to fight in the battleline with battleships.The class possessed a mixed armament of two twin 14.0 in 41st Year Type guns and two twin 8.0 in 41st Year Type guns. The top speed of the class was 22.5 kn and 21.25 kn sustained top speed. The armour protection of the ships were also notable, possessing an armour belt of up to 7 in, 9 in on the primary gun turrets and 8 in thick armour plate on the conning tower. These strong characteristics would mean the Ibukis would be the most advanced armoured cruisers in the world, until the the British Royal Navy unveiled construction of HMS Invincible, a large cruiser so powerful, that it rendered all previous armoured cruiser, obsolete, including the Ibuki and Kurama, before either were launched. Ibuki was completed in Novemember 1909 and Kurama was completed February 1911.

Although inferior to the Invincible-class battlecruiser (except in armour), in August 1912 the navy reclassifed the two vessels as battlecruisers, emphasising their battleship like qualities in comparison to other contemporary armoured cruisers which were still outclassed Ibuki class ships. Both vessels would later took part in various minor engagements during the First World War, notably the hunt for the SMS Emden (1908) and the occupation of German New Guinea. Both ships would fall victim to the tonnage limitations of the Washington naval treaty. The ships were disarmed in 1922 and sold for scrap on 20 September 1923.

Kongō class


The four Kongō-class battlecruiser ships were the first battlecruisers ordered by the Imperial Japanese Navy. The four ships were authorised in 1910 as part of the Emergency Naval Expansion Bill, in response to the construction of HMS Invincible by the British Royal Navy. Designed by British naval architect George Thurston, the first ship of the class (Kongō) was constructed in Britain by Vickers, with the remaining three built in Japan. They were armed with eight 14.0 in main guns, could sail at 27 knots, and were considered to "outclass all other contemporary ships". Kongō was completed in August 1913, Hiei in August 1914, and Haruna and Kirishima in April 1915. The vessels saw minor patrol duty during the First World War.

In the aftermath of the Washington Naval Treaty, all four ships underwent extensive modernisation in the 1920s and 1930s, which reconfigured them as fast battleships. The modernisations strengthened their armour, equipped them with seaplanes, overhauled their engine plant, and reconfigured their armament. With a top speed of 30 kn and efficient engine plants, all four were active in the Second World War; Hiei and Kirishima sailed with the carrier strikeforce to attack Pearl Harbor, while Kongō and Haruna sailed with the Southern Force to invade Malaya and Singapore. Hiei and Kirishima were lost during the Naval Battle of Guadalcanal, Kongō was torpedoed on 21 November 1944 in the Formosa Strait, and Haruna was sunk during the Bombing of Kure on 28 July 1945.

Amagi class


As part of the Eight-Eight fleet, four Amagi-class battlecruisers were planned. The order for these ships and four battleships of the Kii class put an enormous strain on the Japanese government, which by that time was spending a full third of its budget on the navy. JAPANESE AIRCRAFT CARRIER Akagi was the first ship to be laid down; construction began on 6 December 1920 at the naval yard in Kure. Amagi followed ten days later at the Yokosuka naval yard. Atago's keel was laid in Kobe at the Kawasaki shipyard on 22 November 1921, while Takao, the fourth and final ship of the class, was laid down at the Mitsubishi shipyard in Nagasaki on 19 December 1921.

The terms of the February 1922 Washington Naval Treaty forced the class' cancellation, but the two closest to completion (Amagi and Akagi) were saved from the scrappers by a provision that allowed two capital ships to be converted to aircraft carriers. However, the 1923 Great Kantō earthquake caused significant stress damage to the hull of Amagi. The structure was too heavily damaged to be usable, and conversion work was abandoned. Amagi was struck from the navy list and sold for scrapping, which began on 14 April 1924. The other two ships, Atago and Takao, were officially cancelled two years later (31 July 1924) and were broken up for scrap in their slipways. Akagi went on as an aircraft carrier to fight in the Second World War, where it was sunk after air attack during the Battle of Midway.

Design B-64/B-65 class


Design B-64 was originally intended to be part of Japan's Night Battle Force, a force that would attack an enemy fleet's outer defence ring of cruisers and destroyers under the cover of darkness. After penetrating the ring, Japanese cruisers and destroyers would launch torpedo attacks on the enemy's battleships. The remainder of the enemy would be finished off by the main fleet in the following day. The B-64s were intended to support the lighter cruisers and destroyers in these nighttime strikes. This strategy was altered when the Japanese learned the specifications of the United States' Alaska-class cruiser large cruisers. The design was enlarged and redesignated B-65; their purpose would now be to screen the main battle fleet against the threat posed by the fast and heavily armed Alaskas. With war looming in 1940, the Japanese focused on more useful and versatile ship types such as aircraft carriers and cruisers; the Japanese defeat at the 1942 Battle of Midway meant that the ships were postponed indefinitely, and with more important strategic considerations to worry about, the ships were never built.