Although the United States had maintained military forces, including a substantial number of indigenous units, in the Philippines since their annexation in 1898, the islands were largely unprepared for hostilities with Japan. This unpreparedness was the result of several factors. As a signatory of the Washington Naval Treaty in 1922, the United States had agreed, in exchange for limitations on Japanese shipbuilding, to halt construction of any new fortifications in its Pacific possessions. For the Philippines this meant that only the islands near the entrance to Manila Bay, principally Corregidor, were well protected. Similarly, the act to grant the Philippines commonwealth status in 1935-with independence scheduled for 1946-meant that the de-fense of the islands had to devolve gradually on the Philippine government despite its limited resources. Reflecting these realities, the U.S. Joint Army and Navy Basic War Plan ORANGE, last updated in April 1941, limited defense of the islands to Manila Bay and critical adjacent areas. If attacked, the U.S. Army garrison was expected to withdraw to the Bataan Peninsula, a tongue of land on Luzon forming the northwestern boundary of Manila Bay, and to the island of Corregidor. The plan did not envision reinforcement or relief of the Philippine garrison. With a small army committed to continental defense and a general agreement that in the event America went to war it would adopt a defeat-Germany-first strategy, the U.S. military had reluctantly concluded that the Philippines must be sacrificed if the Japanese attacked.