The Ground Observer Corps was a series of Civil Defense programs in the United States to protect against air attack. First begun in World War II by the Army Air Forces, the 1.5 million civilian observers at 14,000 coastal observation posts used naked eye and binocular searches to find invading German and Japanese aircraft. The program ended in 1944.
In early 1950, the Continental Air Command formed a new 8,000 post civilian Ground Observer Corps to supplement what would become the NORAD system. Over 200,000 volunteers participated in nationwide drills, telephoning dozens of coordination centers which in turn relayed information to the Air Defense Command (ADC) ground control interception centers.
By 1952 the program was expanded with a new organizational plan named Operation Skywatch with over three-quarters of a million volunteers taking shifts at over 16 thousand posts and 75 relay centers.
By the late 1950s, a major semi-automatic aircraft warning and detection system had been developed, Semi Automatic Ground Environment (SAGE), and was in the early stages of installation. Due to the dramatic technological improvements provided by this new system, the Air Force canceled the Ground Observer Corps program in 1959.