At the start of 1971 South Vietnamese troops continued operations against the North Vietnamese People's Army of Vietnam (PAVN) and Vietcong (VC) base areas in eastern Cambodia. The ill-conceived and poorly executed Operation Lam Son 719 against PAVN supply lines in eastern Laos showed the weaknesses within the South Vietnamese military command and the limited ability of South Vietnam's armed forces to conduct large-scale combined arms operations. The U.S. continued its unilateral withdrawal from South Vietnam despite the lack of any progress in the Paris Peace Talks and by November U.S. forces had ceased offensive operations. The U.S. withdrawal and antiwar sentiment within the military led to an ongoing decline in morale and discipline within the U.S. forces and growing drug use, particularly of heroin. As U.S. combat units withdrew, security in their former operational areas deteriorated and the PAVN/VC began a series of attacks on ARVN positions in Quảng Trị province and the Central Highlands. In Cambodia the Cambodian government continued to lose ground to the PAVN despite extensive U.S. air support and training and periodic attacks into Cambodia by the ARVN. While the bombing of North Vietnam had ceased in November 1968, U.S. aircraft continued to conduct reconnaissance flights over the North and responded to radar-tracking and antiaircraft fire with "protective reaction" strikes which numbered more than 100 by the year-end and culminated in a five-day bombing campaign in late December.