The Battle of Leyte Gulf, also called the "Battles for Leyte Gulf", and formerly known as the "Second Battle of the Philippine Sea", is generally considered to be the largest naval battle of World War II and, by some criteria, possibly the largest naval battle in history.

It was fought in waters near the Philippine islands of Leyte, Samar from 23–26 October 1944, between combined US and Australian forces and the Imperial Japanese Navy. On 20 October, United States troops invaded the island of Leyte as part of a strategy aimed at isolating Japan from the countries it had occupied in South East Asia, and in particular depriving its forces and industry of vital oil supplies. The Imperial Japanese Navy (IJN) mobilized nearly all of its remaining major naval vessels in an attempt to defeat the Allied invasion, but was repulsed by the U.S. Navy's 3rd and 7th Fleets. The IJN failed to achieve its objective, suffered very heavy losses, and never afterwards sailed to battle in comparable force. The majority of its surviving heavy ships, deprived of fuel, remained in their bases for the rest of the Pacific War.

The Battle of Leyte in the Pacific campaign of World War II was the invasion and conquest of the island of Leyte in the Philippines by American and Filipino guerrilla forces under the command of General Douglas MacArthur, who fought against the Imperial Japanese Army in the Philippines led by General Tomoyuki Yamashita from 20 October - 31 December 1944. The battle launched the Philippines campaign of 1944–45 for the recapture and liberation of the entire Philippine Archipelago and to end almost three years of Japanese occupation. This was also the first battle in which the Japanese used kamikaze pilots.

The Philippines were an important source of supplies, especially rubber, to Japan and also commanded the sea routes to Borneo and Sumatra by which petroleum was brought to Japan: holding on to the Philippines was vital. For the U.S., capturing the Philippines was a key strategic step in isolating Imperial Japan's military holdings in China and the Pacific theater. It was also a personal matter for MacArthur: two years previously he had left the Philippines vowing to return, and he insisted that it was a moral obligation of the U.S. to liberate it as soon as possible.

Leyte (also Northern Leyte; Filipino: Hilagang Leyte) is a province of the Philippines located in the Eastern Visayas region. Its capital is Tacloban City and occupies the northern three-quarters of the Leyte Island. Leyte is located west of Samar Island, north of Southern Leyte and south of Biliran. To the west of Leyte across the Camotes Sea is Cebu Province.

The explorer Ruy López de Villalobos, first came to the island in 1543 and named it Las Islas Felipinas.

During World War II under the Japanese Occupation, the 9th and 92nd Infantry Division of the Philippine Commonwealth Army was reestablished from 1942 to 1946 at the military general headquarters and military camps and garrisoned in Tacloban and Ormoc before the liberation of the Philippines was the military unit organization and started by the Anti-Japanese military operations in the province of Leyte from 1942 to 1945 to helping the local guerrilla groups under by Colonel Ruperto Kangleon and the American liberating forces and fought against the Japanese Imperial forces.