On July 27–28, 1944, Roosevelt had approved MacArthur’s argument that the next objective in the Pacific theatre of the war should be the Philippine Archipelago (which was comparatively near to the already conquered New Guinea). The initial steps toward the Philippines were taken almost simultaneously, in mid-September 1944: MacArthur’s forces from New Guinea seized Morotai, the northeasternmost isle of the Moluccas, which was on the direct route to Mindanao, southernmost landmass of the Philippines; and Nimitz’ fleet from the east landed troops in the Palau Islands.

Already by mid-September the Americans had discovered that the Japanese forces were unexpectedly weak not only on Mindanao but also on Leyte, the smaller island north of the Surigao Strait. With this knowledge they decided to bypass Mindanao and to begin their invasion of the Philippines on Leyte. On October 17–18, 1944, American forces seized offshore islets in Leyte Gulf, and on October 20 they landed four divisions on the east coast of Leyte.

The threat to Leyte was the signal for the Japanese to put into effect their recently formulated plan “Sho-Go” (“Operation Victory”), whereby the Allies’ next attempts at invasion were to be countered by concerted air attacks. Though in the case of Leyte the Japanese Army and Navy air forces in the immediate theatre numbered only 212 planes, it was hoped that the dispatch of four carriers under Vice Admiral Ozawa, with 106 planes, southward from Japanese waters would lure the U.S. aircraft carriers away from Leyte Gulf and that the suicidal “kamikaze” tactics of the Japanese airmen would save the situation. (Kamikaze pilots deliberately crashed their bomb-armed planes into enemy ships.) At the same time, however, a Japanese naval force from Singapore was to sail to Brunei Bay and there split itself into two groups that would converge on Leyte Gulf from the north and from the southwest: the stronger group, under Vice Admiral Kurita Takeo, would enter the Pacific through the San Bernardino Strait between the Philippine islands of Samar and Luzon; the other, under Vice Admiral Nishimura Teiji, would pass through the Surigao Strait.

Kurita’s fleet (five battleships, 12 cruisers, 15 destroyers) lost two of its heavy cruisers to U.S. submarine attack on October 23, when it was off Palawan; and one of the mightiest of Japan’s battleships, the Musashi, was sunk by aerial attack the next day. On October 25, however, Kurita made his way unopposed through the San Bernardino Strait, since the commander of the U.S. 3rd Fleet, Admiral Halsey, had diverted his main strength toward the bait dangled by Ozawa farther to the north. Three groups of U.S. escort carriers, met by Kurita on his way toward Leyte Gulf, suffered heavy damage; but, meanwhile, Nishimura’s fleet (two battleships, one heavy cruiser, four destroyers) had been detected on its way to the Surigao Strait and, on its entry into Leyte Gulf in the early hours of October 25, had been practically annihilated by the U.S. 7th Fleet. Kurita consequently turned back from his rendezvous in Leyte Gulf; and the Japanese defeat in the war’s greatest naval confrontation was sealed by Ozawa’s losses to Halsey: all of his four carriers, together with a light cruiser and two destroyers. The Japanese Navy’s “Sho-Go” as it transpired in the Battle of Leyte Gulf had not only failed to inflict serious damage on the Americans but had resulted in serious losses for the Japanese. These losses amounted to three battleships, one large aircraft carrier, three light carriers, six heavy cruisers, four light cruisers, and 11 destroyers, while the United States lost only one light carrier, two escort carriers, and three destroyers. The battle reduced the Japanese Navy to vestigial strength and cleared the way for the U.S. occupation of the Philippines.

Defeat in the gulf, however, did not prevent the Japanese from landing reinforcements on the west coast of Leyte. They put up so stubborn a resistance that the Americans themselves had to be reinforced before Ormoc fell on December 10, 1944; it was not before December 25 that the Americans could claim control of all Leyte—though there was still some mopping up to be done. Altogether, the defense of Leyte cost the Japanese some 75,000 combatants killed or taken prisoner.

From Leyte the Americans proceeded first, on December 15, to the invasion of Mindoro, the largest of the islands immediately south of Luzon. Kamikaze counterattacks made this conquest more costly; and they were to be continued after the Americans had surprised the Japanese by landing, on January 9, 1945, at Lingayen Gulf on the west coast of Luzon itself, the most important island of the Philippines. The local Japanese commander, Lieutenant General Yamashita Tomoyuki, with no hope of reinforcement, opted for tying the enemy forces down as long as possible by a static defense in three mountainous sectors—west, northwest, and east of the Central Plains behind Manila.

Manila itself was also strongly defended by the Japanese. One U.S. corps, however, was approaching it from Lingayen over the Central Plains; a second corps was landed at Subic Bay, at the northern end of the Bataan Peninsula, on January 29, 1945, to make contact with the former corps at Dinalupihan a week later; and troops made an amphibious landing at Nasugbu, south of Manila Bay, on January 31. Manila was then invested, and during the siege the bay was cleared by the occupation of the southern tip of Bataan Peninsula on February 15 and by the reduction of Corregidor Island in the following fortnight. On March 3 Manila fell at last to the Americans.

The Japanese resistance on Luzon continued in the mountains, and east of Manila it went on until mid-June 1945. Mindanao, meanwhile, was likewise being reduced. A U.S. division landed at Zamboanga, on the southwestern peninsula, on March 10, 1945, and a corps began the occupation of the core of the island on April 17.

The last phase of the U.S. campaign in the Philippines coincided with the opening of the reconquest of Borneo from the Japanese, chiefly by Australian forces. Tarakan Island, off the northeast coast, was invaded on May 1; Brunei on the northwest coast was invaded on June 10; and Balikpapan, on the east coast far to the south of Tarakan, was attacked on July 1. The subsequent collapse of the Japanese defenses around Balikpapan deprived Japan of the oil supplies of southern Borneo.