was the second and last dreadnought battleship built for the Imperial Japanese Navy (IJN) at the end of World War I. She continued to serve through World War II until an internal explosion killed 1,121 of the people on board.
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 most of the 1,474 people on board, with only 353 survivors. 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 artifacts 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 .Skwiot 2008, p. 4 The ship displaced at standard load and at full load.Whitley, p. 200 Her crew consisted of 1,333 officers and enlisted men as built and 1,368 in 1935.Jentschura, Jung & Mickel, p. 28 The crew totaled around 1,475 men in 1942.Stille, p. 34
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.Skwiot 2008, pp. 6, 9–10, 71–72
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, giving her a range of at a speed of . The ship exceeded her designed speed of during her sea trials, reaching at .
During a refit in 1924 the fore funnel was rebuilt in a serpentine shape in an unsuccessful effort to prevent smoke interference with the bridge and fire-control systems. That funnel was eliminated during the ship's 1930s reconstruction when all of her existing boilers were replaced by ten lighter and more powerful oil-fired Kampon boilers, which had working pressures of and temperatures of .Skwiot 2008, pp. 73, 76–77 In addition her turbines were replaced by lighter, more modern, units. When Mutsu conducted her post-reconstruction trials, she reached a speed of with .Skwiot 2008, p. 78 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 .
Armament Mutsus eight 45-caliber guns were mounted in two pairs of twin-gun, superfiring turrets fore and aft. Numbered one to four from front to rear, the hydraulically powered turrets gave the guns an elevation range of −2 to +35 degrees. The rate of fire for the guns was around two rounds per minute. A special Type 3 Sankaidan incendiary shrapnel shell was developed in the 1930s for anti-aircraft use.Campbell, p. 175 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,Skwiot 2008, p. 19 which increased the guns' maximum range from .Friedman, p. 269
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.Skwiot 2008, p. 24 Anti-aircraft defence was provided by four 40-calibre 3rd Year Type AA guns in single mounts. These guns had a maximum elevation of +75 degrees, and a rate of fire of 13 to 20 rounds per minute.Campbell, p. 198 The ship was also fitted with eight torpedo tubes, four on each broadside, two above water and two submerged.Skwiot 2008, p. 31
Around 1926, the four above-water torpedo tubes were removed and the ship received three additional 76 mm AA guns that were situated around the base of the foremast.Skwiot 2008, p. 70 The 76 mm AA guns were replaced by eight 40-calibre dual-purpose guns in 1932,Hackett, Kingsepp, & Ahlberg fitted on both sides of the fore and aft superstructures in four twin-gun mounts.Whitley, p. 202 When firing at surface targets, the guns had a range of ; they had a maximum ceiling of at their maximum elevation of +90 degrees. Their maximum rate of fire was 14 rounds a minute, but their sustained rate of fire was around eight rounds per minute.Campbell, pp. 192–193 Two twin-gun mounts for licence-built Vickers 2-pounder () "pom-pom" light AA guns were also added to the ship in 1932. These guns had a maximum elevation of +80 degrees, which gave them a ceiling of .Skwiot 2008, pp. 26, 30 They had a maximum rate of fire of 200 rounds per minute.Campbell, p. 200
The two-pounders were replaced by 1941 by 20 licence-built Hotchkiss Type 96 light AA guns in five twin-gun mounts.Skwiot 2008, Sheet 8 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".Stille, p. 11 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.
Armour The ship's waterline armour belt was thick and tapered to a thickness of at its bottom edge; above it was a strake of armour. The main deck armour was while the lower deck was thick.Skwiot 2008, pp. 10–11 The turrets were protected with an armour thickness of 305 mm on the face, on the sides, and on the roof. The barbettes of the turrets were protected by armour 305 mm thick, and the casemates of the 140 mm guns were protected by 25 mm armour plates. The sides of the conning tower were thick.
The new 41 cm turrets installed during Mutsus reconstruction were more heavily armoured than the original ones. Face armour was increased to , the sides to , and the roof to .Campbell, p. 182 The armour over the machinery and magazines was increased by 38 mm on the upper deck and 25 mm on the upper armoured deck. These additions increased the weight of the ship's armour to , 32.6 percent of her displacement.Stille, p. 32 In early 1941, in preparation for war, Mutsus barbette armour was reinforced with armour plates above the main deck and plates below it.Chesneau, p. 172
Aircraft Mutsu had an additional boom added to the mainmast in 1926 to handle the Yokosuka E1Y floatplane recently assigned to the ship. In 1933 a catapult was fitted between the mainmast and Turret No. 3,Skwiot 2008, p. 57 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.Skwiot 2008, pp. 54, 57, 70
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.Skwiot 2008, pp. 34, 72
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.Skwiot 2008, pp. 33–37
Construction and service
Mutsu, named for Mutsu Province,Silverstone, p. 334 was laid down at the Yokosuka Naval Arsenal on 1 June 1918 and launched on 31 May 1920. Funding for the ship had partly come from donations from schoolchildren.Hyde, p. 78 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.Skwiot 2008, pp. 17–19, 21 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.
On 4 September 1923, Mutsu loaded supplies at Uchinoura Bay, Kyushu, for the victims of the Great Kantō earthquake. With her sister Nagato, she sank the hulk of the obsolete battleship on 7 September 1924 during gunnery practice in Tokyo Bay, in accordance with the Washington Naval Treaty.Skwiot 2007, pp. 34, 71 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.