On 18 March 1970, Cambodia's chief of state, Prince Norodom Sihanouk, was overthrown by the National Assembly led by the pro-American Defense Minister, General Lon Nol). The government had promptly demanded the removal of all People's Army of Vietnam troops from its territory. The deadline was set for 13 March. These forces had occupied the eastern border region contiguous with the Republic of Vietnam for the previous ten years. These border sanctuaries and Base Areas were of strategic significance to the North Vietnamese effort in South Vietnam, however, and they were not going to give them up without a fight. General Creighton Abrams, U.S. commander in Saigon was pleased by the turn of events in Cambodia. Although Lon Nol had not immediately attacked PAVN, he was much more amenable to the U.S. than had been the mercurial Sihanouk. For the past year and half, Abrams had also been bombarded by requests for the authorization of airstrikes by the highly-secret Military Assistance Command, Vietnam Studies and Observations Group or SOG. SOG's reconnaissance teams had been conducting operations "over the fence" in Cambodia for three years but could still not obtain close air support, either to cover their operations or to strike lucrative PAVN logistical targets in the Base Areas.
Operation Patio
On 18 April, Abrams requested authority from the Joint Chiefs of Staff to utilize U.S. tactical aircraft based in South Vietnam for a 30-day period. These aircraft would be acting in concert with Operation Menu, the highly classified bombing of PAVN sanctuaries and Base Areas in eastern Cambodia by USAF B-52 bombers. Two days later the Joint Chiefs granted his request. All communications and messages concerning the operation were to be sent through special, secure channels and aircraft conducting the missions were assigned cover targets in Laos in the same way that the B-52s of Menu were assigned false targets in South Vietnam. The first strike of the operation was launched on 24 April and plans called for the operation to last for only 30 days, until the third week of May. The aircraft were authorized to strike targets in northeastern Cambodia extending west of the South Vietnamese border. On 25 April, the boundary was extended to a depth of. The onset of the Cambodian Campaign by U.S. and South Vietnamese forces on 29 April forced an early termination on 4 May after only 156 had been flown. Operation Patio was quickly superseded by the much more extensive and destructive Operation Freedom Deal.
