The United States and Philippine Commonwealth military forces, with naval and air support from Australia and the Mexican 201st Fighter Squadron, were progressing in liberating territory and islands when the Japanese forces in the Philippines were ordered to surrender by Tokyo on 15 August 1945, after the dropping of the atomic bombs on mainland Japan and the Soviet invasion of Manchuria.

By mid-1944, American forces were only 300 nautical miles (560 km) southeast of Mindanao, the largest island in the southern Philippines – and able to bomb Japanese positions there using long-range bombers.

Aircraft carrier-based warplanes were already conducting air strikes and fighter sweeps against the Japanese in the Philippines, especially their military airfields.

[d][20] With victories in the Marianas campaign (on Saipan, on Guam, and on Tinian, during June and July 1944), American forces were getting close to Japan itself.

While remaining loyal to the United States, many Filipinos hoped and believed that liberation from the Japanese would bring them freedom and their already-promised independence.

The only contributions by the U.S. Marine Corps in this campaign were USMC aircraft and aviators, who greatly helped to provide air cover for the U.S. Army soldiers and assisted U.S. Army Air Forces aircraft, and one small USMC artillery unit, V Amphibious Corps (VAC) Artillery, commanded by Brigadier General Thomas E. Bourke.

The U.S. Sixth Army continued its advance from the east, as the Japanese rushed reinforcements to the Ormoc Bay area on the western side of the island.

The Filipino guerrillas also performed valuable service in maintaining public order and in keeping the roads and highways free of congestion.

After the American beachheads were established, the Leyte guerrilla groups were attached directly to the Sixth Army corps and divisions to assist in scouting, intelligence, and combat operations.

[25][failed verification] With the initial U.S. Sixth Army landings on the beaches at Tacloban and Dulag, Colonel Ruperto Kangleon's units went into action.

They dynamited key bridges to block Japanese displacement toward the target area; they harassed enemy patrols; and they sabotaged supply and ammunition depots.

Information on enemy troop movements and dispositions sent from guerrilla outposts to Kangleon's Headquarters was dispatched immediately to Sixth Army.

Mindoro was also the location of another breakthrough: the first appearance during the War in the Pacific of USAAF squadrons flying the fast, long-range P-51B Mustang fighters.

On 9 January 1945, on the south shore of Lingayen Gulf on the western coast of Luzon, General Krueger's Sixth Army landed his first units.

With heavy air support, Army units pushed inland, taking Clark Field, 40 miles (64 km) northwest of Manila, in the last week of January.

The Americans needed to establish a major harbor base at Manila Bay to support the expected invasion of Japan, planned to begin on 1 November 1945.

[29] In all, ten U.S. divisions and five independent regiments battled on Luzon, making it the largest American campaign of the Pacific war, involving more troops than the United States had used in North Africa, Italy, or southern France.

Throughout the Philippines, U.S. forces were aided by Filipino guerrillas to find and dispatch the holdouts,[30] the last of whom, Hiroo Onoda, did not surrender until 1974, in the mountains of Lubang Island in Mindoro.

As at many Pacific Islands, major Japanese officials, including members of the Imperial Family, visited in person to convince the soldiers that they must surrender by order of the Emperor.