The Philippines campaign (, , ), also known as the Battle of the Philippines () or the Fall of the Philippines, was from December 8, 1941, to May 8, 1942, the invasion of the Philippines by the Empire of Japan and the defense of the islands by United States and the Philippine Armies during World War II. The Japanese launched the invasion by sea from Formosa, over north of the Philippines. The defending forces outnumbered the Japanese by a ratio of 3:2 but were a mixed force of non-combat-experienced regular, national guard, constabulary and newly created Commonwealth units. The Japanese used first-line troops at the outset of the campaign, and by concentrating their forces, they swiftly overran most of Luzon during the first month. The Japanese high command, believing that they had won the campaign, made a strategic decision to advance by a month their timetable of operations in Borneo and Indonesia and to withdraw their best division and the bulk of their airpower in early January 1942.<ref>[http://www.history.army.mil/books/wwii/MacArthur%20Reports/MacArthur%20V2%20P1/ch6.htm#p103 Japanese Operations in the Southwest Pacific Area – Reports of General MacArthur Volume II] , p. 104.</ref> That, coupled with the defenders' decision to withdraw into a defensive holding position in the Bataan Peninsula and also the defeat of three Japanese battalions at the "Battle of the Points" and "Battle of the Pockets", enabled the Americans and Filipinos to hold out for four more months. After the Japanese failure to penetrate the Bataan defensive perimeter in February the Japanese conducted a 40-day siege. The crucial large natural harbor and port facilities of Manila Bay were denied to the Japanese until May 1942. While the Dutch East Indies operations were unaffected, this heavily hindered the Japanese offensive operations in New Guinea and the Solomon Islands, buying time for the U.S. Navy to make plans to engage the Japanese at Guadalcanal instead of much further east. Japan's conquest of the Philippines is often considered the worst military defeat in US history. About 23,000 American military personnel and about 100,000 Filipino soldiers were killed or captured. Background Japanese activity Objectives The Japanese planned to occupy the Philippines as part of their plan for a "Greater East Asia War" in which their Southern Expeditionary Army Group seized sources of raw materials in Malaya and the Netherlands East Indies while the Combined Fleet neutralized the United States Pacific Fleet. Five years earlier, in 1936, Captain Ishikawa Shingo,