The Battle of Leyte Gulf (Filipino: Labanan sa golpo ng Leyte, lit.'Battle of Leyte gulf'; Japanese: , romanized: Reite oki Kaisen, lit.'Leyte Open Sea Naval Battle') was the largest naval battle of World War II and by some criteria the largest naval battle in history, with over 200,000 naval personnel involved. It was fought in waters near the Philippine islands of Leyte, Samar, and Luzon from 23 to 26 October 1944 between combined American and Australian forces and the Imperial Japanese Navy (IJN), as part of the invasion of Leyte, which aimed to isolate Japan from the countries that it had occupied in Southeast Asia, a vital source of industrial and oil supplies.

By the time of the battle, Japan had fewer capital ships (aircraft carriers and battleships) left than the Allied forces had total aircraft carriers, which underscored the disparity in force strength at that point in the war. Regardless, the IJN mobilized nearly all of its remaining major naval vessels in an attempt to defeat the Allied invasion, but it was repulsed by the US Navy's Third and Seventh Fleets.

The battle consisted of four main separate engagements (the Battle of the Sibuyan Sea, the Battle of Surigao Strait, the Battle off Cape Engao, and the Battle off Samar), as well as lesser actions.It was the first battle in which Japanese aircraft carried out organized kamikaze attacks, and it was the last naval battle between battleships in history. The Japanese Navy suffered heavy losses and never sailed in comparable force thereafter since it was stranded for lack of fuel in their bases for the rest of the war and so it could not affect the successful Allied invasion of Leyte.

Musashi (武蔵), named after the former Japanese province, was one of three Yamato-class battleships 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, displacing almost 72,000 long tons (73,000 t) fully loaded and armed with nine 46-centimetre (18.1 in) main guns. Their secondary armament consisted of four 15.5-centimetre (6.1 in) triple-gun turrets formerly used by the Mogami-class cruisers. They were equipped with six or seven floatplanes to conduct reconnaissance.

Commissioned in mid-1942, Musashi was modified to serve as the flagship of the Combined Fleet, and spent the rest of the year working up. The ship was transferred to Truk in early 1943 and sortied several times that year with the fleet in unsuccessful searches for American forces. She was used to transfer forces and equipment between Japan and various occupied islands several times in 1944. Torpedoed in early 1944 by an American submarine, Musashi was forced to return to Japan for repairs, during which the navy greatly augmented her anti-aircraft armament. She was present during the Battle of the Philippine Sea in June, but did not come in contact with American surface forces. During the Battle of Leyte Gulf, Musashi was sunk by an estimated 19 torpedo and 17 bomb hits from American carrier-based aircraft on 24 October 1944. Over half of her crew was rescued. Her wreck was located in March 2015 by a team of researchers employed by Microsoft co-founder Paul Allen.