Tonopah Air Force Station was initially part of Phase II of the Air Defense Command Mobile Radar program. The Air Force approved this expansion of the Mobile Radar program on October 23, 1952. Radars in this network were designated “SM.” One AN/FPS-90 was retired in 1969. The Air Force inactivated the 866th Radar Squadron 1 July 1970 as a result of budget restrictions, and the general phase down of air defense radar stations.