BRIDGES ON BATAAN: Foundation for a temporary bridge is prepared.

The defense of Bataan began officially on 7 January 1942. On that day Wainwright assumed command of the West Sector of the Bataan Defense Force, which became I Philippine Corps, and the East Sector, redesignated II Philippine Corps, came under General Parker, till then commander of the entire Bataan Defense Force. The boundary between the two corps bisected the length of the peninsula from Mt. Natib to the Mariveles Mountains. The tip of Bataan south of the Mariveles Mountains was designated the Service Command Area and responsibility for its defense given to Brig. Gen. Alien C. McBride, MacArthur's deputy for the Philippine Department. To Wainwright's corps was assigned the defense of the western half of Bataan; Parker's corps was on the Manila Bay side. Both corps were under MacArthur's headquarters on Corregidor, which by 5 January had established a Bataan echelon under Brig. Gen. R. J. Marshall. Through Marshall's headquarters, consisting of officers from the general and special staff sections of USAFFE, it was possible for MacArthur to exercise close control over operations on Bataan. "I am on my main battle line," MacArthur told the War Department on 7 January, "awaiting general attack." The defense of Bataan was conceived as a defense in depth. The first line, called the main battle position, extended from Mabatang, a short distance north of Abucay, on the east, across Mt. Natib to Mauban on the west coast, a distance of twenty miles. A strong outpost line of resistance was established in front of the main battle position and defenses to a depth of several miles were prepared to the rear. Along the beaches on both coasts troops were posted to guard against amphibious envelopment.

In Wainwright's corps on the west were three Philippine Army divisions, the 1st, 31st, and 91st, to which was attached the combat elements of the 71st Division (PA); the 26th Cavalry (PS); a battery each of field artillery and 75-mm. guns (SPM), and miscellaneous troops-altogether about 22,500 men. On the right (east), in Parker's corps, were four more Philippine Army divisions, the 11th, 21st, 41st, and 51st; supporting artillery; and the 57th Infantry (PS) from the Philippine Division. General Parker had about 25,000 men in his corps.

Eight miles behind the main battle position, paralleling the Pilar-Bagac road, was the rear battle position which in prewar plans had formed the main line of the Bataan defenses. On 7 January this line was not yet fully organized; while the forces along the main battle position held back the enemy, other troops would prepare this position. Posted along this line and assigned the task of organizing it for a last-ditch defense was the USAFFE reserve, the Philippine Division (less 57th Infantry), the tank group, and a group of 75-mm. SPM's. Corps and USAFFE artillery was emplaced to cover the front lines as well as the beach defenses in all sectors.

South of the rear battle position was the Service Command Area. Under McBride's command was a variety of troops: the 2d Division (PC), organized on 7 January and composed of Constabulary troops, the remaining elements of the 71st Division (PA), including the division headquarters, provisional infantry units formed from air corps troops, and a provisional battalion of bluejackets and marines.

The Mabatang-Mauban line, or Abucay- Mauban line, as it was more generally called, the main battle position, occupied on 7 January, was not a continuous line. Separating and forming an almost impenetrable barrier between the left portion held by I Corps and the right portion held by II Corps was the northernmost of the two extinct volcanoes, covering an area about fifteen by fifteen miles. Around the crater are steep and jagged peaks rising to a height of 3,000 to 4,000 feet. The northernmost peak, Mt. Santa Rosa, is 3,052 feet high. About three and a half miles southeast is the highest point on the crater's edge, Mt. Natib. In a distance of 2,000 yards this 4,222-foot-high mountain drops to half its height. Mt. Silanganan, to the southwest, is 3,620 feet high. On its west escarpment this land mass drops a thousand feet in as many yards. Though the military crests of these mountains provided ideal defensive positions- one officer called them "an infantryman's dream"-they made effective mutual support between the two corps impossible. The Mt. Natib position was selected, despite its known limitations, because strategy required that a stand be made here to gain time to prepare the rear battle position and to retain as long as possible the lateral communication provided by the Pilar-Bagac road.