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When MacArthur returned to active duty, the latest revision plans for the defense of the Philippine Islands had been completed in April 1941 and was called WPO-3, based on the joint Army-Navy War Plan Orange of 1938, which involved hostilities between the United States and Japan. Under WPO-3, the Philippine garrison was to hold the entrance to Manila Bay and deny its use to Japanese naval forces and ground forces were to prevent enemy landings. If the enemy prevailed, they were to withdraw to the Bataan Peninsula, which was recognized as the key to the control of Manila Bay. It was to be defended to the "last extremity". In addition to the regular U.S. Army troops, the defenders could rely on the Philippine Army, which had been organized and trained by General MacArthur.