Ibuki - class cruiser The cruisers " ' were the last class of heavy cruiser s built for the Imperial Japanese Navy ( IJN ) . In order to save design time , the ships were essentially repeats of the earlier . Begun during World War II , only the lead ship , " Ibuki " , was launched , but was in the process of being converted into a light aircraft carrier when construction was suspended in 1945 . She was scrapped beginning in 1946 . The unnamed second ship was scrapped less than a month after being laid down in order to clear her slipway for an aircraft carrier . Design and description . The design of the " Ibuki " class was a minor improvement over the last pair of the " Mogami " class after those ships had been upgraded during the late 1930s . The main improvement was the replacement of the triple torpedo tube mounts in the older ships with quadruple mounts . They cost 60 , 000 , 000 yen each and had a crew of 54 officers and 822 enlisted men . The ships had a length of overall . They had a beam of and a draft of . They displaced at standard load and at ( full load ) . They were fitted with four Kampon geared steam turbine sets with a total of , each driving a propeller . Steam was provided by eight Kampon Ro Gō - type three - drum water - tube boilers that operated at a pressure of and temperature of . The ships had a designed speed of . They carried of fuel oil which gave them an estimated range of at . Electrical power was supplied by three turbo generator s and two diesel generators . Armament . The main armament of the " Ibuki " class was intended to be ten 50 - caliber 20 cm 3rd Year Type No . 2 guns mounted in twin turrets , three forward and two aft of the superstructure , numbered one through five from the bow to the stern . The first two forward turrets were on the same level , but the third turret could superfire over the first two . The guns could depress to −5° and had a maximum elevation of 55° . They fired projectiles at a muzzle velocity of . They had a maximum range of at an elevation of 45° and the ship carried 128 rounds per gun . The secondary armament was to consist of eight 40 - caliber 12 . 7 cm Type 89 anti - aircraft ( AA ) guns in twin mounts . They fired projectiles at a rate between 8 and 14 rounds per minute at a muzzle velocity of ; at 45° , this provided a maximum range of , and a maximum ceiling of . The ships were also intended to be equipped with four twin 25 mm Type 96 light AA guns abreast the funnel . They fired projectiles at a muzzle velocity of ; at 50° , this provided a maximum range of , and an effective ceiling of . The maximum effective rate of fire was only between 110 and 120 rounds per minute due to the frequent need to change the fifteen - round magazines . Two twin 13 . 2 mm Type 93 machine gun mounts were supposed to be mounted on the bridge with 2 , 000 rounds per gun . The " Ibuki " - class ships were intended to be armed with four rotating quadruple Type 92 torpedo tube s , two on each broadside . The ship carried 24 Type 93 torpedo s , 16 in the tubes and 8 in reserve . Quick - reloading gear was installed for every mount that allowed the reserve torpedoes to be loaded in three to five minutes in ideal conditions . The Type 93 torpedo , fueled by compressed oxygen and widely referred to in post - war literature as the " Long Lance " , had three range / speed settings . It had a range of at a speed of , at , or at a speed of . Before " Ibuki " was launched , one proposal was made to replace the aircraft and their equipment with five quintuple Type 0 torpedo tube mounts . Two of these would be mounted on each side and the last on the centerline , but nothing was done . Fire control , sensors and aircraft . Two Type 94 fire - control director s , one atop the bridge and the other abaft the funnel , were going to be fitted to control the main guns . They used range data received from three coincidence rangefinder s . Two of these were to be installed in turrets Nos . 3 and 4 while the primary rangefinder was mounted above the bridge . A pair of Type 94 high - angle directors , one on each side of the bridge , were intended to control the Type 89 guns . Each director was fitted with a rangefinder . The 25 mm guns would have been controlled by two Type 95 directors mounted on the bridge . Early warning would have been provided by a Type 2 , Mark 2 , Model 1 air search radar mounted at the top of the foremast . A Type 93 passive hydrophone system would have been fitted in the bow . The ships were designed to carry three aircraft on a platform between the funnel and the mainmast . These would have consisted of one three - seat Aichi E13A and two two - seat Yokosuka E14Y floatplane s . They would have been launched by a pair of Kure Type 2 aircraft catapult s , one on each side of the aircraft platform . The ships would have carried a total of 122 powder charges for the catapults as well as four bombs for the aircraft . Armor . The ships ' armor scheme was only slightly modified from the " Mogami " - class cruisers . Their waterline armoured belt extended all the way down to the double bottom . It extended from the forward to the rear magazine s below the fore and aft turrets and was angled inwards at the top 20° from the vertical to improve its resistance to horizontal shellfire . Over the machinery spaces , it was thick at the top and tapered to at the bottom . The outer ends of the fore and aft machinery compartments was protected by a transverse bulkhead . On the sides of the magazines , the belt was thick and tapered to 30 mm at the bottom . The magazines were protected by fore and aft transverse bulkheads thick . The steering gear and the rudder compartments had sides that consisted of plates and their ends were protected by of armor . The deck above the steering gear and rudders was thick . The thickness of the armored deck ranged from on the flat and on the slope . The sides of the conning tower were 100 millimeters thick while its roof was thick . The main gun turret s had of armor on all sides and on the roof . The barbette armor ranged from in thickness . The ammunition hoists for the secondary armament were protected by of armor . The funnel uptakes were provided with of armor . There was no separate anti - torpedo bulkhead as that function was performed by the lower extension of the belt armor . Ships . The two " Ibuki " - class cruisers were ordered in November 1941 as part of the IJN ' s Rapid Naval Armaments Supplement Programme ( マル急計画 , 出師準備第一着作業建艦計画 Maru Kyū Keikaku , Suishi - Junbi Dai - Ichi Chakusagyō Kenkan Keikaku ? ) . Both ships were laid down without names , just as Warships No . 300 and No . 301 , but the former was named " Ibuki " on 5 April 1943 . No . 301 was ordered scrapped less than a month after she was laid down in order to clear her slipway for the carrier which was laid down on 1 October 1942 . After her launch , the construction of " Ibuki " was suspended in July 1943 while her fate was discussed . A possible conversion to a fast oiler was considered until the Navy decided on 25 August to convert her to a light aircraft carrier at Sasebo Naval Arsenal . Work on the conversion did not begin until the incomplete hull was towed to Sasebo on 21 December . It was originally intended to complete her in March 1945 , but this was extended until August . Construction was suspended on 16 March , when the ship was about 80 % complete , to allow for the construction of small submarines . " Ibuki " was scrapped at Sasebo from 22 November 1946 to 1 August 1947 .