During her 1934–1936 reconstruction, the ship's stern was lengthened by 7.55 metres (24 ft 9 in) to improve her speed, and her forward superstructure was rebuilt into a pagoda mast.

The turbines were designed to produce a total of 80,000 shaft horsepower (60,000 kW), 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.

[3] 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.

[8] Additional fuel oil was stored in the bottoms of the newly added torpedo bulges, which increased her capacity to 5,560 t (5,470 long tons) and thus her range to 8,560 nmi (15,850 km; 9,850 mi) at 16 knots.

The manually operated guns had a maximum range of 20,500 metres (22,400 yd) and fired at a rate of six to ten rounds per minute.

[14] 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.

[22] 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.

3,[27] 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.

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 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 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.

With her sister Nagato, she sank the hulk of the obsolete battleship Satsuma on 7 September 1924 during gunnery practice in Tokyo Bay, in accordance with the Washington Naval Treaty.

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.

[16] In June 1942 Mutsu, commanded by Rear Admiral Gunji Kogure, was assigned to the main body of the 1st Fleet during the Battle of Midway, together with Yamato, Nagato, Hōshō, the light cruiser Sendai, nine destroyers, and four auxiliary ships.

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.

Two days later, the ship departed Yokosuka accompanied by the cruisers Atago, Takao, Maya, Haguro, Yura, and Myōkō, the seaplane tender Chitose, and escorting destroyers to support operations during the Guadalcanal Campaign.

[40] 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.

On 7 January 1943, Mutsu departed from Truk for Japan via Saipan, accompanied by the carrier Zuikaku, the heavy cruiser Suzuya and four destroyers.

[16] On 8 June 1943, Mutsu was moored in the Hashirajima fleet anchorage, with 113 flying cadets and 40 instructors from the Tsuchiura Naval Air Group aboard for familiarisation.

A massive influx of water into the machinery spaces caused the 150-metre (490 ft) forward section of the ship to capsize to starboard and sink almost immediately.

The 45-metre (148 ft) stern section upended and remained floating until about 02:00 hours on 9 June before sinking, coming to rest a few hundred feet south of the main wreck at coordinates 33°58′N 132°24′E / 33.967°N 132.400°E / 33.967; 132.400.

[41] The nearby Fusō immediately launched two boats which, together with the destroyers Tamanami and Wakatsuki and the cruisers Tatsuta and Mogami, rescued 353 survivors from the 1,474 crew members and visitors aboard Mutsu; 1,121 men were killed in the explosion.

[42] 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.

[16] To avert the potential damage to morale from the loss of a battleship so soon after the string of recent setbacks in the war effort, Mutsu's destruction was declared a state secret.

[16] At the time of the explosion, Mutsu's magazine contained some 16-inch Type 3 "Sanshikidan" incendiary shrapnel anti-aircraft shells, which had caused a fire at the Sagami arsenal several years earlier due to improper storage.

Because they might have been the cause of the explosion, the minister of the navy, Admiral Shimada Shigetaro, immediately ordered the removal of Type 3 shells from all IJN ships carrying them, until the conclusion of the investigation into the loss.

[47] Historian Mike Williams put forward an alternative theory of fire: A number of observers noted smoke coming from the vicinity of No.

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.

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.

Despite the fact that the salvaged components were remarkably preserved, in particular the two gun turrets, bow (including chrysanthemum mount) and stern (with every propeller, and intact rudders and steering gear), the ship was broken up for her low-background steel and sold to an anonymous "research institute.