Amagi - class battlecruiser The was a series of four battlecruiser s planned for the Imperial Japanese Navy as part of the so - called Eight - eight fleet . The ships were to be named " Amagi " , , " Atago " , and " Takao " ( initially named ) , after the mountains Amagi , Akagi , Atago , and Takao . The " Amagi " design was essentially a lengthened version of the battleship , but with a thinner armored belt and deck and a modified secondary battery arrangement . Limitations imposed by the 1922 Washington Naval Treaty prevented the class from being completed as designed . However , the treaty had a limited allowance for hulls already under construction to be converted into aircraft carrier s . " Amagi " and " Akagi " were both intended for conversion , but an earthquake damaged the hull of " Amagi " so extensively that the ship was scrapped . " Akagi " was reconstructed as an aircraft carrier and served with distinction as part of the " Kido Butai " during the Second World War , participating in the Japanese attack on Pearl Harbor before being sunk at the Battle of Midway . Design . Dimensions and machinery . The ships had a planned displacement of and at a full load . The class design was 820 ft 3 in ( 250 m ) long at the waterline , and 826 ft 1 in ( 251 . 8 m ) overall . The ships would have had a beam of 101 ft ( 30 . 8 m ) and a draft of 31 ft ( 9 . 5 m ) and would have used four propeller shafts , powered by Gihon turbines . The design staff intended to use turbine engines , which were to be powered by 19 Kampon water - tube boilers , eleven of which were oil - fired , while the other eight were to have mixed oil and coal for fuel . This system was designed to provide for a top speed of . The planned fuel stores amounted to 3 , 900 tons of oil and 2 , 500 tons of coal . The ships had a planned cruising speed of , and with full fuel stores , the ships would have had a maximum range of . Armament . The ships were to be equipped with a main battery of ten 16 in ( 406 mm ) L / 45 guns in five twin turrets , although an L / 50 gun tested in 1920 might have been implemented instead . The guns fired 2 , 205 lb ( 1 , 000 kg ) armor - piercing projectiles with a 494 lb ( 224 kg ) propellant charge at 2 , 592 ft / s ( 790 m / s ) , at a rate of fire between 1 . 5 to 2 . 5 rounds per minute . Each gun had 90 rounds and an approximate barrel life of 250 – 300 shots . The turrets would have been arranged along the centerline : two superfiring turrets fore , and three in line aft of the superstructure . The gun turrets weighed 1 , 004 tons ( 1 , 020 mt ) , and allowed for depression of −5 degrees and elevation of 30 degrees . The secondary battery was to have consisted of sixteen 5 . 5 in ( 140 mm ) L / 50 guns mounted in casemate s along the center of the ship . These guns fired 83 . 8 lb ( 38 . 0 kg ) projectiles and used 22 . 8 – 24 . 2 lb ( 10 . 33 – 10 . 97 kg ) of propellant at a muzzle velocity of 2 , 789 – 2 , 805 ft / s ( 850 – 855 m / s ) . The guns had a maximum elevation of 25 degrees , which enabled a maximum range of . Four , later increased to six , 4 . 7 in ( 120 mm ) L / 45 anti - aircraft guns were to have been mounted amidships , along with eight 24 in ( 610 mm ) above - water torpedo tubes . Armor . It was planned that the " Amagi " class would be protected by a main belt 10 in ( 254 mm ) thick , sloped at 12 degrees , and a torpedo bulkhead 2 . 875 in ( 73 mm ) thick . The main battery barbette s were designed to have between 9 and 11 in ( 229 – 280 mm ) of armor plating , and the conning tower would have had armor ranging in thickness from 3 in ( 76 mm ) to a maximum of 14 in ( 356 mm ) . Deck armor was to have been 3 . 875 in ( 98 mm ) thick . Background . Experiences in the Russo - Japanese War convinced naval war planners that more fast capital ships were needed , so on 4 April 1907 , the Imperial Defence Council approved an " Eight - eight " policy . This plan originally called for a fleet of eight battleship s and eight armored cruiser s that would all be under ten years old ( later changed to eight battlecruiser s and reduced to eight years old ) . However , the advent of the dreadnought battleship crippled this plan at the beginning ; given Japan ' s weak and underdeveloped economy and the enormous strain that had been put on it during the Russo - Japanese War ( Japan emerged from the war victorious , but bankrupt ) , the launch of was a " disaster " for Japan . In 1907 , Japan was halfway to the eight - eight , with two newly delivered battleships ( the ) in the fleet and two more ( the ) and four armored cruisers authorized or under construction . In addition , three more battleships and four armored cruisers had been authorized , though not funded . However , naval technology was changing ; older battleships , including all of Japan ' s battleships in commission or under construction , were quickly rendered obsolete with the commissioning of HMS " Dreadnought " ( hence the terms dreadnought and pre - dreadnought ) , and armored cruisers were seemingly useless in the face of the new battlecruisers being laid down by Great Britain and Germany . The Imperial Japanese Navy ( IJN ) recognized this , and proposed in 1909 that two battlecruisers be ordered from British plans , with one to be built in Great Britain and one to be built at home . These two ships became the . In 1910 , there was still authorization for one battleship and four armored cruisers . This battleship , a more heavily armored version of the " Kongō " - class battlecruisers , became Japan ' s first super - dreadnought , . With these ships , Japan appeared to be getting closer to the eight - eight goal ; however , these new ships represented a " new level of naval strength " for the IJN , and they made all previous Japanese capital ships obsolete . This meant that any naval planner aiming for an eight - eight fleet would have to call for seven more battleships and four more battlecruisers at a time when Japan was trying to weather a worldwide economic depression . After proposals from the IJN in 1911 and 1912 for massive shipbuilding programs , the Cabinet compromised down to a " four - four " plan ; under this , three new battleships and no new battlecruisers were authorized . The Navy did not agree , and instead called for an " eight - four " fleet , while the Imperial Defence Council called for the original eight - eight . The Cabinet relented , and by July 1914 , it was decided to aim first for an eight - four fleet , followed by the eight - eight fleet . The eight - four plan was presented to the Diet of Japan in 1915 ; it aimed to have the eight battleships and four battlecruisers by 1923 with the building of two and two s . The problem with this was that the old plan intended all of the ships of the eight - eight fleet to be under eight years old ; by the time these new ships were completed , " Fusō " and the first two " Kongō " ships would be past their replacement age . The plan was approved in 1917 , along with funding for two battlecruisers which became the " Amagi " class . In late 1917 , the Navy proposed to expand the eight - four plan by adding two more battlecruisers ; this was approved , and two more " Amagi " - class ships were ordered . However , having eight 16 in ( 406 mm ) gun ships ( four battleships and four battlecruisers ) on order put an enormous financial strain on Japan , which was spending about a third of its national budget on the Navy . The massive size and scale of its building program was rapidly driving up the cost of naval construction and armament . Construction , cancellation , and conversion . was the first ship of the class 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 . The projected completion dates for the first pair of ships were December and November 1923 , respectively . " Atago " was laid down in Kobe at the Kawasaki shipyard on 22 November 1921 , and was projected to be finished in December 1924 . " Takao " , the fourth and final ship of the class , was laid down at the Mitsubishi shipyard in Nagasaki on 19 December 1921 , and was also projected to be completed in December 1924 . The Washington Naval Treaty , signed in February 1922 , greatly reduced the tonnage allowed for capital ships in the signatory nations . The treaty also instituted a moratorium on new warship construction ; battlecruisers canceled under this included one class each from Japan , the United States , and Great Britain : the " Amagi " class , the and the G3 class , respectively . The treaty did allow for battleship and battlecruiser hulls currently under construction to be converted into aircraft carriers , but only if these new carriers were kept under a 27 , 000 - ton limit . Considering that the " Amagi " class were designed to displace at full load in their battlecruiser configuration , this would have been a rather difficult displacement to obtain . However , the Americans also had the same problem when designing a conversion of their " Lexington " class , so an exception , spearheaded by US Assistant Secretary of the Navy Theodore Roosevelt , Jr . , was added to the treaty that gave the five signatories the option of converting up to two capital ships that were under construction to 33 , 000 - ton aircraft carriers . This resulted in the United States and Japan quickly reordering two ships each . Japan chose " Amagi " and " Akagi " , the two ships nearest to completion , for conversion . The September 1923 Great Kantō earthquake in Tokyo 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 stricken from the navy list and sold for scrapping , which began on 14 April 1924 . The other two ships , " Atago " and " Takao " , were officially canceled two years later ( 31 July 1924 ) and were broken up for scrap in their slipways . The incomplete , on which work had stopped on 5 February 1922 , was reordered as a carrier to replace " Amagi " . " Akagi " s career as an aircraft carrier . The conversion of " Akagi " began on 19 November 1923 , and was completed in March 1927 . However , the strange assortment of flight decks fitted on " Akagi " — a main landing deck superimposed over two short take - off decks — proved unsatisfactory , and the ship was withdrawn from active service in 1935 for modernization . The lower two flight decks were removed , the main deck was lengthened to 817 ft ( 249 m ) , and a third elevator was added . Refitting was completed in 1938 . " Akagi " supported operations off China in early 1939 and 1940 , and underwent an overhaul in November 1940 . " Akagi " served as Vice Admiral Chūichi Nagumo ' s flagship in the attack on Pearl Harbor on 7 December 1941 . Nagumo ' s " Kido Butai " — composed of the carriers " Akagi " , " Kaga " , , , , and , supported by escorts — launched two waves of airstrikes on the American base at Pearl Harbor in a devastating surprise attack . American losses included four battleships and two destroyers sunk and nearly 200 aircraft destroyed . On 19 February 1942 , aircraft from " Akagi " , " Hiryū " , " Sōryū " , and " Kaga " participated in the bombing of Darwin , Australia . On 27 February , their bombers severely damaged the old American carrier , which was subsequently scuttled by her escort . " Akagi " and the carriers " Hiryū " and " Sōryū " were sent in March 1942 with a mixed force of battleships , cruisers , and destroyers to the Indian Ocean to engage the British fleet there and to support planned attacks on Ceylon . In the Easter Sunday Raid on 5 April , aircraft from the carriers struck the British base at Colombo , destroying a number of aircraft and sinking an armed merchant cruiser and the old destroyer in the harbor . The Japanese fleet also spotted the heavy cruisers and at sea ; both ships were sunk in an overwhelming air attack . On 9 April the carriers attacked British installations at Trincomalee , destroying aircraft and sinking the carrier , the destroyer , and the corvette . Battle of Midway . In late May 1942 , in an effort to draw out and destroy the elusive American carriers , Japanese forces organized attacks on the Aleutian Islands in Alaska and Midway Atoll in the Western Pacific . Nagumo , aboard " Akagi " , led " Kaga " , " Sōryū " , and " Hiryū " and the support ships of the First Carrier Striking Force to Midway . In the initial attack , Japanese planes neutralized a small force of fighter aircraft and inflicted heavy damage to American installations . Torpedo planes and dive - bombers sent from Midway to harry the Japanese fleet had little effect , but the Japanese attack plan had been deciphered by codebreakers , and the American carriers ' planes were already en route . Torpedo bombers from , , and joined the attack in succession , forcing the Japanese carriers to maneuver violently to avoid torpedoes and rendering them unable to launch additional aircraft . American dive - bombers , arriving late after difficulty locating the fleet , soon landed fatal strikes on " Akagi " , " Kaga " , and " Sōryū " . " Yorktown " , handicapped by hits from " Hiryū " s bombers , managed to return to the fight only to take two torpedo hits a couple of hours later . The burning " Yorktown " was abandoned , but her scouts pinpointed " Hiryū " s location , and bombers from " Enterprise " put " Hiryū " out of action with four bomb strikes . Japan lost all four carriers of the First Carrier Striking Force at Midway .