Tosa - class battleship The were two dreadnought s ordered as part of the " Eight - Eight " fleet for the Imperial Japanese Navy ( IJN ) during the early 1920s . The ships were larger versions of the preceding , and carried an additional twin - gun turret . The design for the class served as a basis for the s . The first ship , , was canceled according to the terms of the Washington Naval Treaty before it could be completed , and was used in experiments testing the effectiveness of its armor scheme before being scuttled in the Bungo Channel . The hull of the second ship , , was converted into an aircraft carrier of the same name . The carrier supported Japanese troops in China during the Second Sino - Japanese War of the late 1930s , and took part in the attack on Pearl Harbor on 7 December 1941 and the invasion of Rabaul in the Southwest Pacific in January 1942 . The following month her aircraft participated in a combined carrier airstrike on Darwin , Australia , during the Dutch East Indies campaign . She was sunk during the Battle of Midway in 1942 . Background . The IJN believed that a modern battle fleet of eight battleships and eight armored cruiser s was necessary for the defense of Japan ; the government ratified that idea in 1907 . This policy was the genesis of the Eight - Eight Fleet Program , the development of a cohesive battle line of sixteen capital ship s less than eight years old . Advances in naval technology represented by the British battleship and the battlecruiser forced the IJN to reevaluate on several occasions which ships it considered " modern " and , in 1911 , it restarted the program with orders for the dreadnoughts and the s . By 1915 , the IJN was halfway to its goal and wanted to order four more dreadnoughts , but the Diet rejected the plan and authorized only the dreadnought and two battlecruisers in the 1916 budget . Later that year American President Woodrow Wilson announced plans for ten additional battleships and six battlecruisers , and the Diet authorized three more dreadnoughts in response the following year : a second — — and two to a modified design , " Tosa " and " Kaga " . Design and description . The IJN began reevaluating the " Nagato " design in light of lessons learned from the Battle of Jutland in May 1916 , experiments evaluating armor protection , and newly acquired information on the protective schemes of British and American capital ships . These lessons highlighted the need for better protection of the main gun turrets and magazines , as well as thicker deck armor to protect against plunging fire . Existing methods of defense against mines and torpedoes had also proved to be inadequate and needed improvement . Eleven new designs were rejected between October and early 1917 before Captain Yuzuru Hiraga , superintendent of shipbuilding and the naval architect in charge of the fundamental design of the ships of the Eight - Eight Fleet , presented a heavily modified version of the " Nagato " design , A - 125 , to be built in lieu of the second ship of the class , " Mutsu " , on 12 June 1917 , well before she was actually laid down . Hiraga ' s design for the ship reflected the latest combat experience as well as incorporating advances in boiler technology . It added an extra twin main - gun turret , using space and weight made available by the reduction of the number of boilers from 21 to 12 while the power remained the same . He reduced the secondary armament from 20 guns to 16 ; they were moved up a deck to improve their arcs of fire and their ability to shoot during heavy weather . To increase the ship ' s protection he proposed to angle the belt armor outwards to improve its resistance to horizontal fire , and to thicken the lower deck armor and the torpedo bulkhead . Hiraga also planned to add anti - torpedo bulge s to improve the ship ' s underwater protection . He estimated that his ship would displace as much as " Nagato " , although it would cost about a million yen more . These changes would have considerably delayed the ship ' s completion and were rejected by the Navy Ministry . The rejected design formed the basis for a much larger battleship , designated as A - 127 , with nearly twice as much armor weight as the " Nagato " s . It was designed to achieve the same speed as the older ships , to allow them to maneuver together as a tactical formation . This design was accepted on 27 March 1918 and became the " Tosa " class . The " Tosa " - class ships had a planned displacement of , and at a full load . They would have been long at the waterline , and overall ; the ships would have had a beam of and a draft of . The " Tosa " class would have had a metacentric height of at normal load . A turbo - electric propulsion system was considered for these ships after the United States announced that the system was a great success in the battleship , and the Japanese estimated that a turbo - electric plant could be installed in the " Tosa " class , which would have given the ships a speed of , a range at full speed , and a range at , but this system was rejected . More conventional Curtis geared steam turbines were chosen , powered by 12 Kampon water - tube boilers , eight of which would have used fuel oil and four of which would have used a mixture of oil and coal . This system would have provided to four propeller shafts for a top speed of . The fuel stores would have amounted to of oil and ; at a speed of 14 knots , this would have enabled a maximum range of . Armament . The " Tosa " - class ships were intended to be armed with a main battery of ten 45 - caliber 41 - centimeter guns in five twin turrets , four of which were superfiring fore and aft . Numbered one through five from front to rear , the hydraulically powered turrets had an elevation range of −2 to + 35 degrees . The rate of fire for the guns was around two rounds per minute . The ships were designed to carry 90 rounds per gun , although space was available for 110 . The guns used Type 91 armor - piercing , capped shells . Each of these shells weighed and had a muzzle velocity of . Also available was a high - explosive shell that had a muzzle velocity of . The ships ' secondary armament of twenty 50 - caliber 3rd Year Type 14 - centimeter guns would have been mounted in casemate s , 12 on the upper sides of the hull and eight in the superstructure . The 3rd Year Type guns had a maximum range of at an elevation of + 35 degrees . Each gun could fire a high - explosive projectile at a rate up to 10 rounds per minute and was provided with 120 rounds . Anti - aircraft defense was provided by four 40 - caliber 3rd Year Type 8 - centimeter AA gun s in single mounts . The high - angle guns had a maximum elevation of + 75 degrees , and a rate of fire of 13 to 20 rounds per minute . They fired a projectile with a muzzle velocity of to a maximum height of . The guns were normally supplied with 250 rounds each , although space was available for a total of 400 rounds per gun . These 3rd Year Type guns were intended to be replaced by four 45 - caliber anti - aircraft guns . The " Tosa " s were intended to mount eight torpedo tube s , four above water and four below . The former were to be provided with two torpedoes each and the latter with three each . Armor . The ships ' armor protection was designed to break up shells from a distance of and the primary armor plates were backed up by splinter bulkheads intended to contain any shell fragments . They would have been protected by a waterline main belt of Vickers cemented armor that sloped outwards 15 degrees at the top . Amidships it would have been thick and thick fore and aft . Approximately of the armor belt was below the waterline . The side armor was closed off at its ends by bulkheads thick . The main battery turrets and the portions of the barbette s above the main deck would have had between of armor plating , and the conning tower walls would have had armor thick and a roof of armor plates . The communications tube below the conning tower would have had walls thick . The middle deck was the primary armored deck and was connected to the top of the armor belt . It would have consisted of a plate of New Vickers non - cemented armor on top of a plate of high - tensile steel ( HTS ) above the engine and boiler rooms . Above the magazine s , the thickness of the HTS plate would have increased to 63 mm . The lower deck would have consisted of two plates of HTS . For the first time in a Japanese ship , the " Tosa " s would have had the lower portion of the single funnel protected by 229 mm of armor . In addition , the funnel openings in the lower deck would have been protected by armor gratings . The ships would have had an internal torpedo bulge to provide protection against underwater explosions . This was backed by a torpedo bulkhead also made up of three layers of HTS and angled outwards to meet the base of the waterline belt . It connected to a splinter bulkhead on the lower deck behind the waterline belt . Behind the torpedo bulge and the splinter bulkhead was another splinter bulkhead 12 . 7 – 19 mm thick . Cancellation and fates . Construction of both ships began in 1920 , but the 1922 Washington Naval Treaty intervened , mandating the cancellation of all capital ships being built . Work stopped on the two " Tosa " - class battleships on 5 February 1922 . After being stricken on 1 April 1924 , " Tosa " s incomplete hull was used to test her armor scheme against long - range naval gunfire , aerial bombs , mines , and torpedoes . Two of the shells fired at her fell short , but deeply penetrated her hull through the thin armor of the torpedo bulge below the waterline armor belt . This sparked an interest in optimizing underwater performance of Japanese shells that culminated in production of the Type 91 armor - piercing shell . Conversely , the IJN took measures to defend against shells of this type when reconstructing its existing battleships during the 1930s , as well as in the designs of the s and the heavy cruiser s of the " Mogami " and es . " Tosa " s torpedo defense system proved able to defeat torpedo warhead s , but not larger ones . After the conclusion of the tests , the ship was scuttled by opening her Kingston valve s on 9 February 1925 in of water in the Bungo Channel after the demolition charges failed to detonate . The battlecruiser , which was being converted to an aircraft carrier under the terms of the treaty , was wrecked in the Great Kantō earthquake in 1923 and rendered unusable . As a result , " Kaga " , which was originally slated to be scrapped , was ordered to be converted in " Amagi " s stead . No work took place until 1925 as new plans were drafted and earthquake damage to the Yokosuka Naval Arsenal was repaired . Although the ship was commissioned on 31 March 1928 , she did not join the Combined Fleet ( " Rengo kantai " ) until 30 November 1929 . Much like the converted , " Kaga " was fitted with two flying - off decks " stepped down " from a flight deck that extended two - thirds of the ship ; in theory , this allowed planes to take off directly from the hangars while other planes landed on the top . As aircraft became heavier during the 1930s , they required longer distances to get airborne and the lower flight decks became useless . " Kaga " s 1935 reconstruction removed the lower two decks and extended the top flight deck to the bow . As completed , the ship had two main hangar decks and a third auxiliary hangar with a total capacity of 60 aircraft . " Kaga " was provided with a heavy gun armament in case she was surprised by enemy cruisers and forced to give battle , but her large and vulnerable flight deck , hangars , and other features made her more of a target in any surface action than a fighting warship . Carrier doctrine was still evolving at this time and the impracticability of carriers engaging in gun duels had not yet been realized . The ship was armed with ten 20 cm / 50 3rd Year Type guns : one twin - gun turret on each side of the middle flight deck and six in casemates aft . " Kaga " s waterline armored belt was reduced from during her reconstruction and her deck armor was also reduced from . The carrier displaced at standard load , and at full load , nearly less than her designed displacement as a battleship . This reduction in her displacement increased her speed to and gave her a range of at . In 1933 – 35 " Kaga " was rebuilt to increase her top speed , improve her exhaust systems , and adapt her flight decks to more modern , heavier aircraft . After the reconstruction , the ship displaced at standard load , better boilers gave her a top speed of , and additional fuel storage increased her range to at and raised her aircraft capacity to 90 . The ten guns , although now all mounted singly in casemates , were retained . " Kaga " s aircraft first supported Japanese troops in China during the Shanghai Incident of 1932 and participated in the Second Sino - Japanese War in the late 1930s . With five other fleet carriers , she took part in the Pearl Harbor raid in December 1941 and the invasion of Rabaul in the Southwest Pacific in January 1942 . The following month her aircraft participated in a combined carrier airstrike on Darwin , Australia , helping secure the conquest of the Dutch East Indies by Japanese forces . She missed the Indian Ocean raid in April as she had to return to Japan for repairs after hitting a reef in February . Following repairs , " Kaga " rejoined the 1st Air Fleet for the attack on Midway Atoll in June 1942 . The IJN was surprised by the appearance of three American carriers and , partly due to Admiral Isoroku Yamamoto ' s plan in which ships were too dispersed to support each other , " Kaga " , along with the other three carriers present , was sunk by aircraft from , and on 4 June .