Ibuki-class cruiser

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.Lacroix and Wells, pp. 540–41, 543, 826

The ships had a length of {{convert|200.6|m|ftin|sp=us}} overall. They had a beam of {{convert|20.2|m|ftin|sp=us}} and a draft of {{convert|6.04|m|ftin|sp=us}}. They displaced {{convert|12220|t|LT|sp=us}} at standard load and {{convert|14828|t|LT|sp=us}} at (full load).Jentschura, Jung and Mickel, p. 87

They were fitted with four Kampon geared steam turbine sets with a total of {{convert|152000|shp|kW|lk=in}}, each driving a {{convert|3.9|m|sp=us|adj=on}} propeller. Steam was provided by eight Kampon Ro Gō-type three-drum water-tube boilers that operated at a pressure of {{convert|22|kg/cm2|kPa psi|0|abbr=on|lk=on}} and temperature of {{convert|300|°C}}. The ships had a designed speed of {{convert|35|kn|lk=in}}. They carried {{convert|2163|t|LT}} of fuel oil which gave them an estimated range of {{convert|6300|nmi|lk=in}} at {{convert|18|kn}}. Electrical power was supplied by three {{convert|300|kW|lk=in|adj=on}} turbo generators and two {{convert|200|kW|adj=on}} diesel generators.Lacroix and Wells, pp. 825–26

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.Lacroix and Wells, p. 542 The guns could depress to −5° and had a maximum elevation of 55°. They fired {{convert|125.85|kg|adj=on}} projectiles at a muzzle velocity of {{convert|840|m/s|abbr=on}}. They had a maximum range of {{convert|29400|yd|m|abbr=on}} at an elevation of 45°Campbell, pp. 185–86 and the ship carried 128 rounds per gun.Lacroix and Wells, p. 543 The secondary armament was to consist of eight 40-caliber 12.7 cm Type 89 anti-aircraft (AA) guns in twin mounts. They fired {{convert|23.45|kg|lb|adj=on|sp=us}} projectiles at a rate between 8 and 14 rounds per minute at a muzzle velocity of {{convert|700|-|725|m/s|ft/s|abbr=on}}; at 45°, this provided a maximum range of {{convert|14800|m|yd|sp=us}}, and a maximum ceiling of {{convert|9400|m|ft|sp=us}}.Campbell, pp. 192–93 The ships were also intended to be equipped with four twin 25 mm Type 96 light AA guns abreast the funnel.Lacroix and Wells, p. 825 They fired {{convert|.25|kg|lb|adj=on|sp=us}} projectiles at a muzzle velocity of {{convert|900|m/s|ft/s|abbr=on}}; at 50°, this provided a maximum range of {{convert|7500|m|yd|sp=us|0}}, and an effective ceiling of {{convert|5500|m|ft|sp=us}}. 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.Campbell, p. 200 Two twin 13.2 mm Type 93 machine gun mounts were supposed to be mounted on the bridge with 2,000 rounds per gun.Lacroix and Wells, pp. 543–44

The Ibuki-class ships were intended to be armed with four rotating quadruple {{convert|61|cm|abbr=on}} Type 92 torpedo tubes, two on each broadside. The ship carried 24 Type 93 torpedoes, 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.Lacroix and Wells, pp. 248, 545 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 {{convert|20000|m|yd|sp=us}} at a speed of {{convert|48|kn}}, {{convert|32000|m|yd|sp=us}} at {{convert|40|kn}}, or {{convert|40000|m|yd|sp=us}} at a speed of {{convert|36|kn}}.Campbell, p. 207 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.Lacroix and Wells, p. 545

Two Type 94 fire-control directors, 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 {{convert|8|m|ftin|adj=on|sp=us}} coincidence rangefinders. 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 {{convert|4.5|m|ftin|adj=on|sp=us}} rangefinder. The 25 mm guns would have been controlled by two Type 95 directors mounted on the bridge.Lacroix and Wells, pp. 468, 546–47

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 floatplanes. They would have been launched by a pair of Kure Type 2 aircraft catapults, 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 {{convert|250|kg|adj=on|sp=us}} bombs for the aircraft.Lacroix and Wells, pp. 542, 545, 547

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 magazines 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 {{convert|100|mm|in|1|sp=us}} thick at the top and tapered to {{convert|30|mm|in|sp=us}} at the bottom. The outer ends of the fore and aft machinery compartments was protected by a {{convert|105|mm|1|sp=us|adj=on}} transverse bulkhead. On the sides of the magazines, the belt was {{convert|140|mm|in|sp=us}} thick and tapered to 30 mm at the bottom. The magazines were protected by fore and aft transverse bulkheads {{convert|95|-|140|mm|1|sp=us}} thick. The steering gear and the rudder compartments had sides that consisted of {{convert|100|mm|1|sp=us|adj=on}} plates and their ends were protected by {{convert|50|mm|1|sp=us}} of armor.

The deck above the steering gear and rudders was {{convert|30|mm|in|sp=us|1}} thick. The thickness of the armored deck ranged from {{convert|35|-|40|mm|1|sp=us}} on the flat and {{convert|60|mm|1|sp=us}} on the slope. The sides of the conning tower were 100 millimeters thick while its roof was {{convert|50|mm|in|sp=us}} thick. The main gun turrets had {{convert|25|mm|in|1|sp=us}} of armor on all sides and on the roof. The barbette armor ranged from {{convert|25|to|100|mm|in|1|sp=us}} in thickness. The ammunition hoists for the secondary armament were protected by {{convert|75|to|100|mm|in|1|sp=us}} of armor. The funnel uptakes were provided with {{convert|70|to|95|mm|in|1|sp=us}} of armor. There was no separate anti-torpedo bulkhead as that function was performed by the lower extension of the belt armor.Lacroix and Wells, pp. 449, 452, 456, 463, 542

The two Ibuki-class cruisers were ordered in November 1941 as part of the IJN's Rapid Naval Armaments Supplement Programme. 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.Lacroix and Wells, pp. 539–40

No. 301 was ordered scrapped less than a month after she was laid down in order to clear her slipway for the carrier {{ship|Japanese aircraft carrier|Amagi||2}} which was laid down on 1 October 1942.Lacroix and Wells, p. 540 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.Lacroix and Wells, pp. 540–41

{{Reflist|2}}

• {{cite book|last=Campbell|first=John|title=Naval Weapons of World War II|year=1985|publisher=Naval Institute Press|location=Annapolis, Maryland|isbn=0-87021-459-4}}
• {{cite book|title=Conway's All the World's Fighting Ships 1922-1946|editor1-last=Chesneau|editor1-first=Roger|publisher=Conway Maritime Press|location=Greenwich|year=1980|isbn=0-85177-146-7}}
• {{cite book| last = Jentschura| first = Hansgeorg| first2 = Dieter |last2=Jung|first3=Peter |last3=Mickel| year = 1977| title = Warships of the Imperial Japanese Navy, 1869–1945| publisher = United States Naval Institute| location = Annapolis| isbn = 0-87021-893-X}}
• {{cite book|last1=Lacroix|first1=Eric|last2=Wells II|first2=Linton |title=Japanese Cruisers of the Pacific War|publisher=Naval Institute Press|location=Annapolis, Maryland|date=1997|isbn=0-87021-311-3 |name-list-style=amp |authorlink2=Linton Wells II}}

{{WWII Japanese ships}}

Category:Cruiser classes

Category:World War II cruisers of Japan

Category:Aircraft carriers of the Imperial Japanese Navy

Category:Ships built by Kure Naval Arsenal

Category:Proposed ships

Category:Postwar Japan