The Philippines had suffered under the Japanese occupation. A highly effective guerrilla campaign controlled sixty percent of the islands, mostly jungle and mountain areas. United States Army General Douglas MacArthur had supplied them by submarine, and sent reinforcements and officers.
More than any other Allied garrison attacked on December 7, 1941, the Philippines were an important target for the Imperial Japanese High Command. Japanese Navy and Army bombers from Formosa attacked in the late morning, and achieved the same success their comrades were enjoying over Pearl Harbor.