The US invasion of Leyte on October 20, 1944, prompted the Japanese to activate plan Shō-1, the defense of the Philippines. The Imperial Japanese Navy would seek a decisive battle in Leyte Gulf, while the Imperial Japanese Army would significantly reinforce its forces on Leyte to fight a decisive battle with the Sixth US Army on the island. American troops invaded the beaches south of Tacloban with limited resistance from the Japanese defenders, allowing MacArthur to make good his promise to return with an iconic photo of him wading ashore alongside Philippine President Sergio Osmeña and members of the SWPA staff. The US and Japanese navies then fought a decisive four-day battle for supremacy in the waters surrounding the Philippines, which the US Third and Seventh Fleets won after some anxious moments in the fighting off the coast of Samar. Japanese kamikazes made their appearance on the final day of the battle, and they would bedevil the US Pacific Fleet from that point onward until the end of the war. After the Battle of Leyte Gulf, the remaining elements of the Imperial Japanese Navy would never again contest the Pacific Ocean.

MacArthur desired to liberate the Philippines, but the issue would be decided by the Joint Chiefs of Staff in Washington. Forces under Admiral Chester W. Nimitz conducted a drive in the Central Pacific that by the summer of 1944 culminated with the seizure of the strategically crucial Mariana Islands. By that time, MacArthur’s forces had taken key points along the northern coast of New Guinea and had conquered the Admiralty Islands, isolating the major Japanese air and naval base at Rabaul. The question for the JCS was what to do once these operations concluded. The major objective would be bounded by Luzon, Formosa, and the China coast, with an invasion of Formosa initially seen as key to the defeat of Japan. MacArthur naturally viewed Luzon as the primary objective, while Admiral Ernest King in Washington and Admiral Nimitz in Hawaii looked towards Formosa. This disparity set off a storm of messages, planning, and controversy from March through September 1944 until the JCS finally decided the issue by deferring the invasion of Formosa and agreeing to allow MacArthur to liberate both Leyte and Luzon and the capital city, Manila.

The Philippines campaign was the largest and costliest waged by the US armed forces in the Pacific during World War II. Central to the campaign is the role played by General Douglas MacArthur, one of the most controversial military leaders in US history. In 1941, Roosevelt needed a commander in the Philippines who could unify the American and Filipino forces and provide the needed energy and strategic acumen to defend the islands against a Japanese invasion. On the same day he signed the embargo against Japan in July 1941, Roosevelt reinstated MacArthur as a general in the US Army and gave him command of a new organization, the US Army Forces in the Far East, which would control all US and Philippine army forces in the region. MacArthur formed a staff, the “Bataan Gang,” that would support him over the long war to come. In the fighting of 1941–1942, MacArthur badly bungled the defense of the Philippines, resulting in the largest mass surrender of forces in US history. MacArthur was able to escape to fight another day in Australia, but, for the troops left behind, three years of desultory and brutal life in Japanese prison camps awaited.

In just nine months, the Philippines campaign isolated the Japanese homeland from its conquered empire to the south, made possible an air and sea blockade to prevent the resources of the Netherlands East Indies from reaching Japan, gained a base equivalent to the British Isles in preparation for the invasion of Japan, liberated the Philippines and its people from Japanese occupation, freed Allied prisoners of war and civilian detainees held in camps, destroyed the majority of the remaining Japanese fleet, and destroyed several thousand aircraft. SWPA undertook eighty-seven amphibious landings – more than in any other theater. SWPA logisticians performed legendary feats of improvisation on a shoestring budget. Air support was crucial to the effectiveness of operations in the Philippines. Japanese atrocities convinced MacArthur to charge Yamashita with war crimes on the basis of command responsibility, for which the Japanese general was tried and executed. Civil affairs units and engineers were crucial to rehabilitating the Philippines, which had been devastated by three years of Japanese occupation and nine months of combat operations.