The Philippines campaign of 1944–45 was the Allied campaign to defeat Japanese forces occupying The Philippines, during World War II. The invasion commenced on 20 October 1944 and hostilities continued until the war’s end.

By mid-1944, American forces were only 300 miles southeast of Mindanao, the southernmost island in the Philippines. Allied forces had advanced across the Central Pacific taking the Gilbert, Marshall and Caroline Islands. Carrier based planes were already conducting strikes against the Philippines. American and Australian ground forces under General Douglas MacArthur, Supreme Commander, Southwest Pacific Area, had isolated the Japanese in mainland New Guinea, and then isolated the huge Japanese base at Rabaul by capturing and creating air and naval facilities across the Southwest Pacific theater. With victories in the Marianas campaign (Saipan, Tinian and Guam, June–July 1944), at Peleliu in the Palau Islands (Aug–Sep 1944), and Battle of Morotai (15–16 September 1944), Allied forces were getting close to Japan itself. From the Marianas, U.S. Army Air Forces could bomb the Japanese home islands for the first time during the war. Although Japan was obviously losing the war, they showed no sign of capitulation or collapse. Because of the close relationship between the Philippines and the United States since 1898, the decision was made to advance the date for the long-awaited return to the Philippines. The new date would be 20 October 1944, two months ahead of the previous target date. The Filipinos (people of the Philippine islands) were ready and waiting for the invasion. After General MacArthur was evacuated from the Philippines in March 1942, the islands fell to the Japanese. The Japanese occupation was harsh, accompanied by atrocities and with large numbers of Filipinos pressed into forced labor. During 1942-1944, MacArthur supplied the Filipino guerrilla resistance by submarine and airdrops, so they could harass the Japanese and keep control of the rural jungle and mountain areas, more than half of the country. While loyal to the U.S., many Filipinos hoped and believed that liberation from the Japanese would bring freedom and an independent country. The Australian government offered MacArthur the services of I Corps of the Australian Army for the Philippines campaign. MacArthur suggested that two Australian divisions be used, each attached to a different US corps, but this was not acceptable to Australian leaders, who wanted significant operational control within a particular area, rather than simply supporting a US corps. As a result, the Australian Army played virtually no part in the campaign. However, many units from the Royal Australian Air Force and Royal Australian Navy were involved.

Leyte On 20 October 1944, the U.S. Sixth Army, supported by naval and air bombardment, landed on the favorable eastern shore of Leyte, one of the three large Philippine Islands, north of Mindanao. The Japanese miscalculated the relative strength of forces and attempted to destroy the landing through a major sea battle in Leyte Gulf, fought on 23–26 October. The decisive naval battle nearly eliminated Japan as a major sea power and only encouraged the invasion of Leyte. 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. While the Sixth Army was reinforced successfully, the U.S. Fifth Air Force was able to devastate the Japanese attempts. In torrential rains and over difficult terrain, the advance continued across Leyte and the neighboring island of Samar to the north. On 7 December 1944, U.S. Army units landed at Ormoc Bay and, after a major land and air battle, cut off the Japanese ability to reinforce and supply Leyte. Although fierce fighting continued on Leyte for months, the U.S. Army was in control.

Luzon On 15 December 1944, landings against minimal resistance were made on the southern beaches of the island of Mindoro, a key location in the planned Lingayen Gulf operations, in support of major landings scheduled on Luzon. 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. Almost 175,000 men followed across the twenty-mile beachhead within a few days. With heavy air support, Army units pushed inland, taking Clark Field, 40 miles northwest of Manila, in the last week of January. Two more major landings followed, one to cut off the Bataan Peninsula, and another, that included a parachute drop, south of Manila. Pincers closed on the city and, on 3 February 1945, elements of the 1st Cavalry Division pushed into the northern outskirts of Manila and the 8th Cavalry passed through the northern suburbs and into the city itself. As the advance on Manila continued from the north and the south, the Bataan Peninsula was rapidly secured. On 16 February, paratroopers and amphibious units assaulted Corregidor, and resistance ended there on 27 February. Despite initial optimism, fighting in Manila was harsh. It took until 3 March to clear the city of all Japanese troops. Fort Drum, a fortified island in Manila Bay near Corregidor, held out until 13 April, when a team went ashore and pumped 3,000 gallons of diesel fuel into the fort, then set charges. No Japanese survived the blast and fire. In all, ten U.S. divisions and five independent regiments battled on Luzon, making it the largest campaign of the Pacific war, involving more troops than the United States had used in North Africa, Italy, or southern France.

End Palawan Island, between Borneo and Mindoro, the fifth largest and western-most Philippine Island, was invaded on 28 February, with landings of the Eighth Army at Puerto Princesa. The Japanese put up little direct defense of Palawan, but cleaning up pockets of Japanese resistance lasted until late April, as the Japanese used their common tactic of withdrawing into the mountain jungles, dispersed as small units. Throughout the Philippines, U.S. forces were aided by Filipino guerrillas to find and dispatch the holdouts, the last of which Hiroo Onoda did not surrender until 1974. The U.S. Eighth Army then moved on to its first landing on Mindanao (17 April), the last of the major Philippine Islands to be taken. Mindanao was followed by invasion and occupation of Panay, Cebu, Negros and several islands in the Sulu Archipelago. These islands provided bases for the U.S. Fifth and Thirteenth Air Forces to attack targets throughout the Philippines and the South China Sea. Following additional landings on Mindanao, U.S. Eighth Army troops continued their steady advance against stubborn resistance. By the end of June, the enemy pockets were compressed into isolated pockets on Mindanao and Luzon where fighting continued until the Japanese surrender on 2 September 1945.