This is the seventeenth monograph dealing with USAF plans, policies, and operations in Southeast Asia. It treats USAF involvement from 1973 up to the defeat of South Vietnam at the end of April 1975. Actual USAF operational involvement spanned only the first seven and a half months of 1973 and the final days of evacuation in 1975. However, the plans for retaliatory air attack against North Vietnam remained in effect throughout, and the South Vietnamese continued to hope that U.S. air power would come to their rescue as it had before. This monograph also attempts to summarize the factors leading up to the fall of South Vietnam and the end of the U.S. involvement.