Outside the city proper two VC battalions attacked the U.S. logistical and headquarters complex at Long Binh Post. Biên Hòa Air Base was struck by a battalion, while the adjacent ARVN III Corps headquarters was the objective of another. Tan Son Nhut Air Base, in the northwestern part of the city, was attacked by three battalions. A combat-ready battalion of ARVN paratroopers, awaiting transport to Da Nang, went instead directly into action supporting the United States Air Force's 377th Security Police Squadron and the U.S. Army's 3rd Squadron, 4th Cavalry Regiment in halting the attack. A total of 35 PAVN/VC battalions, many of whose troops were undercover cadres who had lived and worked within the capital or its environs for years, had been committed to the Saigon objectives. By dawn most of the attacks within the city center had been eliminated, but severe fighting between VC and allied forces erupted in the Chinese neighborhood of Cholon around the Phú Thọ racetrack, southwest of the city center, which was being used as a staging area and command and control center by the PAVN/VC. Bitter and destructive house-to-house fighting erupted in the area. On 4 February, the residents were ordered to leave their homes and the area was declared a free fire zone. Fighting in the city came to a close only after a fierce battle between the ARVN Rangers and PAVN forces on 7 March.