of the U.S. 43rd Infantry (Philippine Scouts) were also made a part of the Mindanao Force. USAFFE's Reserve Force, under MacArthur's direct control, was composed of the Philippine Division, the 91st Division (PA), and headquarters units from the PA and Philippine Department, positioned just north of Manila. The 192nd and 194th Tank Battalions formed the separate Provisional Tank Group, also under MacArthur's direct command, at Clark Field/Fort Stotsenburg, where they were positioned as a mobile defense against any attempt by airborne units to seize the field. Four U.S. Coast Artillery Corps regiments guarded the entrance to Manila Bay, including Corregidor Island. Across a narrow 3 kilometre (2 mi) strait of water from Bataan on Corregidor was Fort Mills, defended by batteries of the 59th and 60th Coast Artillery Regiments (the latter an anti-aircraft unit), and the 91st and 92nd Coast Artillery Regiments (Philippine Scouts) of the Harbor Defenses of Manila and Subic Bays. The 59th CA acted as a supervisory unit for the batteries of all units positioned on Forts Hughes, Drum, Frank, and Wint. The majority of the forts had been built circa 1910–1915 and, except for Fort Drum and Battery Monja on Corregidor, were unprotected against air and high-angle artillery attack except by camouflage. The USAFFE's aviation arm was the Far East Air Force (FEAF) of the U.S. Army Air Forces, commanded by Maj. Gen. Lewis H. Brereton. Previously the Philippine Department Air Force and Air Force USAFFE, the air force was activated on November 16, 1941, and was the largest USAAF combat air organization outside the United States. Its primary combat power in December 1941 consisted of 91 serviceable P-40 Warhawk fighters and 34 B-17 Flying Fortress bombers, with further modern aircraft en route. Tactically the FEAF was part of the Reserve Force, so that it fell under MacArthur's direct command. As of November 30, 1941, the strength of US Army Troops in the Philippines, including Philippine units, was 31,095, consisting of 2,504 officers and 28,591 enlisted (16,643 Americans and 11,957 Philippine Scouts). Mobilization MacArthur's mobilization plans called for induction of the ten reserve divisions between September 1 and December 15, 1941. The timetable was met on September 1 with the induction of one regiment per division, but slowed as a lack of facilities and equipment hampered training. The second regiments of the divisions were not called up until November 1, and the third regiments were not