was forced to withdraw after taking heavy casualties with no hope of sufficient reinforcements. By nightfall, December 23, the Japanese had moved ten miles (16 km) into the interior. The next day, 7,000 men of the 16th Division hit the beaches at three locations along the shore of Lamon Bay in southern Luzon, where they found General Parker's forces dispersed, and without artillery protecting the eastern coast, unable to offer serious resistance. They immediately consolidated their positions and began the drive north toward Manila where they would link up with the forces advancing south toward the capital for the final victory. Withdrawal into Bataan The U.S. Philippine Division moved into the field in reaction to reports of airborne drops near Clark Field, and when this proved false, were deployed to cover the withdrawal of troops into Bataan and to resist Japanese advances in the Subic Bay area. On December 24, MacArthur invoked the prewar plan WPO-3 (War Plan Orange 3), which called for use of five delaying positions in central Luzon while forces withdrew into Bataan. This was carried out in part by the 26th Cavalry Regiment. He relieved General Parker of his command of South Luzon Force and had him begin preparing defensive positions on Bataan, using units as they arrived; both the military headquarters and the Philippine's government were moved there. Nine days of feverish movement of supplies into Bataan, primarily by barge from Manila, began in an attempt to feed an anticipated force of 43,000 troops for six months. (Ultimately 80,000 troops and 26,000 refugees flooded Bataan.) Nevertheless, substantial forces remained in other areas for several months. On December 26, Manila was declared an open city by MacArthur. However, the United States military was still using the city for logistical purposes while the city was declared open and the Japanese army ignored the declaration and bombed the city. Units of both defense forces were maneuvered to hold open the escape routes into Bataan, in particular San Fernando, the steel bridges at Calumpit over the deep Pampanga River at the north end of Manila Bay, and Plaridel north of Manila. The South Luzon Force, despite its inexperience and equivocating orders to withdraw and hold, successfully executed "leapfrogging" retrograde techniques and crossed the bridges by January 1. Japanese air commanders rejected appeals by the 48th Division to bomb the bridges to trap the retreating forces, which were subsequently demolished