was one of four planned s built for the Imperial Japanese Navy (IJN), beginning in the late 1930s. The Yamato-class ships were the heaviest and most powerfully armed battleships ever constructed, Musashi had a length of between perpendiculars and overall. She had a waterline beam of and a draught of at deep load. She displaced at standard load and at deep load. Her crew consisted of 2,500 officers and ratings in 1942, and about 2,800 in 1944.
The battleship had four sets of Kampon geared steam turbines, each of which drove one propeller shaft. The turbines were designed to produce a total of , using steam provided by 12 Kampon water-tube boilers, giving the ship a maximum speed of . She had a stowage capacity of of fuel oil, giving a range of at a speed of . The ship's secondary battery consisted of twelve 60-calibre 155-millimetre 3rd Year Type guns mounted in four triple turrets, one each fore and aft of the superstructure and one on each side amidships. These had become available once the Mogami-class cruisers were rearmed with 20 cm/50 3rd Year Type naval gun| guns. Heavy anti-aircraft defence was provided by a dozen 40-calibre 127-millimetre (5 in) Type 89 dual-purpose guns in six twin turrets, three on each side of the superstructure. Musashi also carried thirty-six 25-millimetre (1 in) Type 96 light anti-aircraft (AA) guns in 12 triple-gun mounts, all mounted on the superstructure. The ship was also provided with two twin mounts for the licence-built Type 93 anti-aircraft machine guns, one on each side of the bridge. Below it was a strake of armour that ranged in thickness from over the magazines and machinery spaces, respectively; it tapered to a thickness of at its bottom edge. The deck armour ranged in thickness from . The turrets were protected with an armour plate thick on the face, on the sides, and 270 millimetres on the roof. The barbettes of the turrets were protected by armour thick, and the turrets of the 155 mm guns were protected by armour plates. The sides of the conning tower were thick and its roof was 200 millimetres thick. Underneath the magazines were armour plates to protect the ship from mine damage. Musashi contained 1,147 watertight compartments (1,065 underneath the armour deck, 82 above) to preserve buoyancy in the event of battle damage.
Aircraft
Musashi was fitted with two catapults on her quarterdeck and could stow up to seven floatplanes in her below-decks hangar. The ship operated Mitsubishi F1M biplanes and Aichi E13A1 monoplanes and used a , stern-mounted crane for recovery.
Fire control and sensors
The ship was equipped with four rangefinders, one atop her forward superstructure and one in each of her main gun turrets, and another unit atop her rear superstructure. Each gun turret was equipped with an rangefinder. Low-angle fire was controlled by two Type 98 fire-control directors mounted above the rangefinders on the superstructure. Type 94 high-angle directors controlled the 127 mm AA guns, with Type 95 short-range directors for the 25 mm AA guns.
Musashi was built with a Type 0 hydrophone system in her bow, usable only while stationary or at low speed. In September 1942, a Type 21 air-search radar was installed on the roof of the 15-metre rangefinder at the top of the forward superstructure. Two Type 22 surface-search radars were installed on the forward superstructure in July 1943. During repairs in April 1944, the Type 21 radar was replaced by a more modern version, and a Type 13 early-warning radar was also fitted.
Construction
thumb|Musashi as she appeared in mid-1944
To cope with Musashis great size and weight, the construction slipway was reinforced, nearby workshops were expanded, and two floating cranes were built. The ship's keel was laid down on 29 March 1938 at Mitsubishi's Nagasaki shipyard, and was designated "Battleship No. 2". Throughout construction, a large curtain made of hemp rope weighing prevented outsiders from viewing construction.
Launching the Musashi also presented challenges. The ship's thick launch platform, made of nine Douglas fir planks bolted together, took two years to assemble (from keel-laying in March 1938) because of the difficulty in drilling perfectly straight bolt holes through 4 metres of fresh timber. The problem of slowing and stopping the massive hull once inside the narrow Nagasaki Harbour was met by attaching of heavy chains on both sides of the hull to create dragging resistance in the water. The launch was concealed by measures that included a citywide air-raid drill staged on launch day to keep people inside their homes. Musashi was launched on 1 November 1940, coming to a stop only further than the hull's expected travel distance across the harbour. The entry of such a large mass into the water caused a wave, which swept the harbour and local rivers, flooding homes and capsizing small fishing boats. Musashi was fitted out at nearby Sasebo, with Captain Kaoru Arima assigned as her commanding officer.
Service
thumb|left|Musashi and Yamato in [[Chuuk Lagoon|Truk Lagoon in early 1943]]
Musashi was commissioned at Nagasaki on 5 August 1942, and assigned to the 1st Battleship Division, together with Yamato, and . Beginning five days later, the ship conducted machinery and aircraft-handling trials near Hashirajima. Her secondary armament of twelve 127 mm guns, 12 triple 25 mm gun mounts, and four anti-aircraft machine guns was fitted 3–28 September 1942 at Kure, as well as a Type 21 radar. The ship was working up for the rest of the year. Arima was promoted to rear admiral on 1 November. and sailed for Truk three days later, arriving on 22 January. On 11 February, she replaced her sister ship Yamato as the fleet's flagship. On 3 April, Yamamoto left Musashi and flew to Rabaul, New Britain to personally direct "Operation I-Go", a Japanese aerial offensive in the Solomon Islands. His orders were intercepted and deciphered by Magic, and American Lockheed P-38 Lightning fighters shot down his transport aircraft and killed him in Operation Vengeance while he was en route from New Britain to Ballale, Bougainville. On 23 April, his cremated remains were flown back to Truk and placed in his cabin on board Musashi. The torpedo hit killed seven crewmen and wounded another eleven. After temporary repairs, Musashi sailed for Japan later that night and arrived at Kure Naval Arsenal on 3 April. From 10 to 22 April, she was repaired, while her anti-aircraft armament was substantially increased in the space freed up by removal of the beam-mounted triple turrets. When she undocked on 22 April, the ship's secondary battery comprised six 15.5 cm guns, twenty-four 12.7 cm guns, one hundred and thirty 25 mm guns, and four 13.2 mm machine guns. She also received new radars (which were still primitive compared to American equipment) and depth-charge rails on her fantail.
The following day, the submarine torpedoed and sank the heavy cruiser near Palawan. The destroyer rescued 769 survivors and transferred them to Musashi later in the day.
Loss at Sibuyan Sea
On 24 October, while transiting the Sibuyan Sea, Kurita's ships were spotted by a reconnaissance aircraft from the fleet carrier . Just over two hours later, the battleship was attacked by eight Curtiss SB2C Helldiver dive bombers from Intrepid at 10:27. One bomb struck the roof of Turret No. 1, failing to penetrate. Two minutes later, Musashi was struck starboard amidships by a torpedo from a Grumman TBF Avenger, also from Intrepid. The ship took on 3,000 tonnes of water and a 5.5-degree list to starboard that was later reduced to 1 degree by counterflooding compartments on the opposite side. During this attack, two Avengers were shot down. and reducing her speed to . At 15:25, Musashi was attacked by 37 aircraft from Intrepid, the fleet carrier and the light carrier . The ship was hit by 13 bombs and 11 more torpedoes during this attack, for a loss of three Avengers and three Helldivers. Her speed was reduced to , her main steering engine was temporarily knocked out and her rudder was briefly jammed 15 degrees to port. Counterflooding reduced her list to six degrees to port from its previous maximum of ten degrees. Musashi had been struck by an estimated total of 19 torpedoes and 17 bombs. and analysis by the US Naval Technical Mission to Japan reports 10 torpedo and 16 bomb hits.|group=N
thumb|Musashi down by the bow after the air attacks, shortly before her sinking
Kurita left Musashi to fend for herself at 15:30, and encountered her again at 16:21 after reversing course. The ship was headed north, with a list of 10 degrees to port, down at the bow with her forecastle awash. He detailed a heavy cruiser and two destroyers to escort her while frantic efforts were made to correct her list, including flooding another engine room and some boiler rooms. Her engines stopped before she could be beached. At 19:15, her list reached 12 degrees and her crew was ordered to prepare to abandon ship, which they did fifteen minutes later when the list reached 30 degrees. Musashi capsized at 19:36 and sank in of water at . Inoguchi chose to go down with his ship; 1,376 of her 2,399-man crew were rescued. About half of her survivors were evacuated to Japan, and the rest took part in the defence of the Philippines.
Wreck
Discovery
For over 70 years after her sinking, various attempts were made by shipwreck hunters to locate the wreck of the Japanese battleship, but none succeeded. Musashi, like other Japanese warships, did not have its name on its sides, making it more difficult for divers and shipwreck hunters to find her. A research team sponsored by Microsoft co-founder Paul Allen eventually found her after eight years of searching for the wreck, going through various historical records in different countries, and deploying the high-tech yacht and a remotely operated vehicle to aid in their search. In March 2015, Allen announced that the team had found Musashi under the Sibuyan Sea, some beneath the surface.
The ship had been thought to have sunk in one piece; in reality, it exploded underwater, scattering debris across the ocean floor. The bow section from the number one barbette forward is upright on the sea floor, while the stern is upside down. The forward superstructure and funnel is detached from the rest of the ship and lies on its port side. In the live streaming video tour conducted by the expedition team, a mount for the seal of the Imperial Japanese Navy—a chrysanthemum made out of teak, long rotted away—can be seen amid the debris. The video also showed damage made by U.S. torpedoes, including a warped bow and hits under the ship's main gun.
Although discovering the shipwreck was very important to the Japanese people because of the presence aboard of over 1,000 Japanese sailors' remains, the National Museum of the Philippines stated that "any further activity [pertaining to the shipwreck would] be governed by established rules and regulations." The Museum pointed out that the wreck site of Musashi, as stated by the law, is considered an archaeological site under Romblon's jurisdiction, and was "giving priority to verifying the discovery, obtaining and sharing key information, facilitating the protection and preservation of the site, and formulating appropriate next steps."