was the second and last dreadnought battleship built for the Imperial Japanese Navy (IJN) at the end of World War I. In 1923 she carried supplies for the survivors of the Great Kantō earthquake. The ship was modernized in 1934–1936 with improvements to her armour and machinery, and a rebuilt superstructure in the pagoda mast style.

Other than participating in the Battle of Midway and the Battle of the Eastern Solomons in 1942, where she did not see any significant combat, Mutsu spent most of the first year of the Pacific War in training. She returned to Japan in early 1943. That June, one of her aft magazines detonated while she was at anchor, sinking the ship with the loss of 1,121 crew and visitors. The IJN investigation into the cause of her loss concluded that it was the work of a disgruntled crew member. The navy dispersed the survivors in an attempt to conceal the sinking in the interest of morale in Japan. Much of the wreck was scrapped after the war, but some artefacts and relics are on display in Japan, and a small portion of the ship remains where she was sunk.

Description

Mutsu had a length of between perpendiculars and overall. She had a beam of and a draught of . The ship displaced at standard load and at full load. Her crew consisted of 1,333 officers and enlisted men as built and 1,368 in 1935. The crew totaled around 1,475 men in 1942.

In 1927, Mutsus bow was remodeled to reduce the amount of spray produced when steaming into a head sea. This increased her overall length by to . During her 1934–1936 reconstruction, the ship's stern was lengthened by to improve her speed, and her forward superstructure was rebuilt into a pagoda mast. She was given torpedo bulges to improve her underwater protection and to compensate for the weight of the additional armour and equipment. These changes increased her overall length to , her beam to and her draught to . Her displacement increased over to at deep load.

Propulsion

Mutsu was equipped with four Gihon geared steam turbines, each of which drove one propeller shaft. The turbines were designed to produce a total of , using steam provided by 21 Kampon water-tube boilers; 15 of these were oil-fired, and the remaining half-dozen consumed a mixture of coal and oil. The ship had a stowage capacity of of coal and of fuel oil, In addition her turbines were replaced by lighter, more modern, units. Additional fuel oil was stored in the bottoms of the newly added torpedo bulges, which increased her capacity to and thus her range to at . The turrets aboard the Nagato-class ships were replaced in the mid-1930s using those stored from the unfinished s. While in storage the turrets were modified to increase their range of elevation to −3 degrees to +43 degrees, which increased the guns' maximum range from .

The ship's secondary armament of twenty 50-calibre guns was mounted in casemates on the upper sides of the hull and in the superstructure. The manually operated guns had a maximum range of and fired at a rate of six to ten rounds per minute. Anti-aircraft defence was provided by four 40-calibre 3rd Year Type These guns had a maximum elevation of +80 degrees, which gave them a ceiling of . They had a maximum rate of fire of 200 rounds per minute.

The two-pounders were replaced by 1941 by 20 licence-built Hotchkiss Type 96 light AA guns in five twin-gun mounts. This was the standard Japanese light AA gun during World War II, but it suffered from severe design shortcomings that rendered it a largely ineffective weapon. According to historian Mark Stille, the twin and triple mounts "lacked sufficient speed in train or elevation; the gun sights were unable to handle fast targets; the gun exhibited excessive vibration; the magazine was too small, and, finally, the gun produced excessive muzzle blast". These 25 mm guns had an effective range of , and a ceiling of at an elevation of 85 degrees. The maximum effective rate of fire was only between 110 and 120 rounds per minute because of the frequent need to change the 15-round magazines. The turrets were protected with an armour thickness of 305 mm on the face, on the sides, and on the roof. The armour over the machinery and magazines was increased by 38 mm on the upper deck and 25 mm on the upper armoured deck. In early 1941, in preparation for war,

Aircraft

Mutsu had an additional boom added to the mainmast in 1926 to handle the Yokosuka E1Y floatplane recently assigned to the ship. and a collapsible crane was installed in a port-side sponson the following year; the ship was equipped to operate two or three seaplanes, although no hangar was provided. The ship was operating Nakajima E4N2 biplanes until they were replaced by Nakajima E8N2 biplanes in 1938. A more powerful catapult was installed in November 1938 to handle heavier aircraft like the single Kawanishi E7K, added in 1939–40. Mitsubishi F1M biplanes replaced the E8Ns on 11 February 1943.

Fire control and sensors

The ship was fitted with a rangefinder in the forward superstructure. Additional and anti-aircraft rangefinders were also fitted, although the date is unknown. The rangefinders in No. 2 and 3 turrets were replaced by 10-metre units in 1932–33.

Mutsu was initially fitted with a Type 13 fire-control system derived from Vickers equipment received during World War I, but this was replaced by an improved Type 14 system around 1925. It controlled the main and secondary guns; no provision was made for anti-aircraft fire until the Type 31 fire-control director was introduced in 1932. A modified Type 14 fire-control system was tested aboard her sister ship in 1935 and later approved for service as the Type 94. A new anti-aircraft director, also called the Type 94, used to control the 127 mm AA guns, was introduced in 1937, although when Mutsu received hers is unknown. The 25 mm AA guns were controlled by a Type 95 director that was also introduced in 1937.

Construction and service

thumb|Mutsu at sea, 1921

Mutsu, named for Mutsu Province, was laid down at the Yokosuka Naval Arsenal on 1 June 1918 and launched on 31 May 1920. While Mutsu was still fitting out, the American government called a conference in Washington, D.C. late in 1921 to forestall the expensive naval arms race that was developing between the United States, the United Kingdom and the Empire of Japan. The Washington Naval Conference convened on 12 November and the Americans proposed to scrap virtually every capital ship under construction or being fitted out by the participating nations. Mutsu was specifically listed among those to be scrapped even though she had been commissioned a few weeks earlier. This was unacceptable to the Japanese delegates; they agreed to a compromise that allowed them to keep Mutsu in exchange for scrapping the obsolete dreadnought , with a similar arrangement for several American dreadnoughts that were fitting out. Mutsu was commissioned on 24 October 1921 with Captain Shizen Komaki in command. Captain Seiichi Kurose assumed command on 18 November and the ship was assigned to the 1st Battleship Division on 1 December. Mutsu hosted Edward, Prince of Wales, and his aide-de-camp and second cousin, Lieutenant Louis Mountbatten, on 12 April 1922 during the prince's visit to Japan. Captain Mitsumasa Yonai, later Prime Minister of Japan, assumed command on 10 November. The ship was transferred to the reserve on 1 December 1925. Mutsu served as flagship of Emperor Hirohito during the 1927 naval manoeuvres and fleet review. Captain Zengo Yoshida relieved Captain Teikichi Hori on 10 December 1928. On 29 March 1929, the ship was assigned to Battleship Division 3, together with three light cruisers. On 15 November 1938, Captain Aritomo Gotō assumed command of the ship. Mutsu was placed in reserve from 15 December 1938 to 15 November 1939. She was refitted in early 1941 in preparation for war; as part of this work, she was fitted with external degaussing coils and additional armour for her barbettes. she sortied for the Bonin Islands, along with Nagato, the battleships , , , and of Battleship Division 2, and the light carrier as distant support for the fleet attacking Pearl Harbor, and returned six days later. On 18 January 1942, Mutsu towed the obsolete armoured cruiser as a target for the new battleship , which promptly sank Nisshin. Following the loss of all four carriers on 4 June, Yamamoto attempted to lure the American forces west to within range of the Japanese air groups at Wake Island, and into a night engagement with his surface forces, but the American forces withdrew and Mutsu saw no action. After rendezvousing with the remnants of the striking force on 6 June, about half of the survivors from the sunken aircraft carriers of the 1st Air Fleet were transferred to Mutsu. She arrived at Hashirajima on 14 June. fired four shells at enemy reconnaissance aircraft, the first and only time her guns were fired in anger during the war. Mutsu returned to Truk on 2 September; a group of skilled AA gunnery officers and men were detached to serve as instructors to ground-based naval anti-aircraft gunners stationed in Rabaul. During October Mutsu off-loaded surplus fuel oil to the fleet oil tanker Kenyo Maru, allowing the tanker to refuel other ships involved in Guadalcanal operations. On 7 January 1943, Mutsu departed from Truk for Japan via Saipan, accompanied by the carrier , the heavy cruiser and four destroyers. Mutsu left Hashirajima for Kure on 13 April, where she prepared to sortie to reinforce the Japanese garrisons in the Aleutian Islands in response to the Battle of the Komandorski Islands. The operation was cancelled the next day and the ship resumed training.

The nearby Fusō immediately launched two boats which, together with the destroyers and and the cruisers and , rescued 353 survivors from the 1,474 crew members and visitors aboard Mutsu; 1,121 men were killed in the explosion. Only 13 of the visiting aviators were among the survivors.

After the explosion, as the rescue operations commenced, the fleet was alerted and the area was searched for Allied submarines, but no traces were found. Some of the survivors were sent to Truk in the Caroline Islands and assigned to the 41st Guard Force. Another 150 were sent to Saipan in the Mariana Islands, where most were killed in 1944 during the battle for the island.

  • Sabotage by a disgruntled crewman. While no individual was named in the commission's final report, its conclusion was that the cause of the explosion was most likely a crewman in No. 3 turret who had recently been accused of theft and was believed to have been suicidal.
  • A midget or fleet submarine attack. Extensive searches immediately following the sinking had failed to detect any enemy submarine, and the Allies had made no attempt at claiming the enormous propaganda value of sinking a capital ship in her home anchorage; consequently, this possibility was quickly discounted. Eyewitnesses also spoke of a reddish-brown fireball, which indicated a magazine explosion; this was confirmed during exploration of the wreck by divers.

The commission issued its preliminary conclusions on 25 June, well before the divers had completed their investigation of the wreck, and concluded that the explosion was the result of a disgruntled seaman. Historian Mike Williams put forward an alternative theory of fire:

<blockquote>A number of observers noted smoke coming from the vicinity of No. 3 turret and the aircraft area just forward of it, just before the explosion. Compared with other nations' warships in wartime service, Japanese battleships contained a large amount of flammable materials including wooden decking, furniture, and insulation, as well as cotton and wool bedding. Although she had been modernized in the 1930s, some of the Mutsus original electrical wiring may have remained in use. While fire in the secure magazines was a very remote possibility, a fire in an area adjacent to the No. 3 magazine could have raised the temperature to a level sufficient to ignite the highly sensitive black-powder primers stored in the magazine and thus cause the explosion.</blockquote>

Salvage operations

thumb|A 14-cm 3rd Year Type gun from Mutsu on display at the Yasukuni Museum

Divers were brought into the area to retrieve bodies and to assess the damage to the ship. Prior to diving on the wreck they were allowed to familiarize themselves on board Mutsus sister ship, Nagato. The Navy leadership initially gave serious consideration to raising the wreck and rebuilding her, although these plans were dropped after the divers completed their survey of the ship on 22 July. Thus Mutsu was struck from the Navy List on 1 September. As part of the investigation, Dive-boat No. 3746, a small Nishimura-class search and rescue submarine, explored the wreck on 17 June with a crew of seven officers. While crawling on the harbour bottom, it became snagged on the wreckage and its crew nearly suffocated before they could free themselves and surface. In July 1944, the oil-starved IJN recovered of fuel from the wreck. The salvagers retrieved 849 bodies of crewmen lost during the explosion. In 1995, the Mutsu Memorial Museum declared that no further salvage operations were planned.

The only significant portion of the ship that remains is a long section running from the bridge structure forward to the vicinity of No. 1 turret. The highest portion of the ship is below the surface.

Surviving artifacts

thumb|Mutsus original 41&nbsp;cm No. 4 turret at the Imperial Japanese Naval Academy, Eta Jima, in 1947

thumb|A gun from Mutsu on display outside the [[Yamato Museum in Kure, Hiroshima]]

In addition to the 140&nbsp;mm gun donated to the Yasukuni Shrine, now on display at the Yasukuni Museum, This is the ship's original turret, removed during her refit in the 1930s. Other artifacts are also on display at the Naval History Museum on the grounds of the former Naval Academy.

  • One 410&nbsp;mm gun from No. 3 turret formerly on display at the Museum of Maritime Science, Shinagawa, in Tokyo
  • A rudder and a section of propeller shaft were on display at the Arashiyama Art Museum until it closed around 1991. The rudder, an anchor and one propeller have been relocated to the JMSDF Kure Museum, directly across the street from the Yamato Museum. The left-side 410&nbsp;mm gun from No. 3 turret is displayed outside as well, in Daiwa Park, Kure. Also on display outside the Yamato Museum entrance in Kure are one of Mutsu's anchors, a fairlead and the stern pennant jackstaff.
  • A part of the number three gun turret's armour is on display at Shide Shrine in Yokkaichi, Mie Prefecture.
  • One of the 410&nbsp;mm guns is on display at the Hijiri Museum in Omi, Nagano.

Notes

Footnotes

References

  • Maritimequest.com: Mutsu photo gallery 19 March 2022 at the Internet Wayback Machine
  • Combinedfleet.com: service history – key dates