Aircraft carrier-based warplanes were already conducting air strikes and fighter sweeps against the Japanese in the Philippines, especially their military airfields. U.S. Army and Australian Army troops under the American General Douglas MacArthur, the Supreme Commander of the Southwest Pacific Theater of Operations, had either overrun, or else isolated and bypassed, all of the Japanese Army on New Guinea and the Admiralty Islands. Before the invasion of the Philippines, MacArthur's northernmost conquest had been at Morotai in the Dutch East Indies on September 15–16, 1944. This was MacArthur's one base that was within bomber range of the southern Philippines.