Semi-Automatic Ground Environment
The Semi-Automatic Ground Environment (SAGE) was a system of large computers and associated networking equipment that coordinated data from many radar sites and processed it to produce a single unified image of the airspace over a wide area. SAGE directed and controlled the NORAD response to a Soviet air attack, operating in this role from the late 1950s into the 1980s. Its enormous computers and huge displays remain a part of cold war lore, and a common prop in movies such as Dr. Strangelove and Colossus.Powering SAGE were the largest computers ever built, IBM's AN/FSQ-7. Each SAGE Direction Center (DC) contained two FSQ-7's for redundancy, filling two floors of a large cube-shaped concrete building. The upper two floors contained offices, operator stations, and a single two-story radar display visible to most of the DC's personnel. Information was fed to the DC's from a network of radar stations as well as readiness information from various defence sites. The computers, based on the raw radar data, developed ""tracks"" for the reported targets, and automatically calculated which defences were within range. Subsets of the data were then sent to the many operator consoles, where the operators used light guns to select targets onscreen for further information, select one of the available defences, and issue commands to attack. These commands would then be automatically sent to the defence site via teleprinter. Later additions to the system allowed SAGE's tracking data to be sent directly to CIM-10 Bomarc missiles and some of the US Air Force's interceptor aircraft in-flight, directly updating their autopilots to maintain an intercept course without operator intervention. Each SAGE DC also forwarded data to a Combat Center (CC) for ""supervision of the several sectors within the division"" (""each combat center [had] the capability to coordinate defense for the whole nation""). Connecting the various sites was an enormous network of telephones, modems and teleprinters.SAGE became operational in the late 1950s and early 1960s at a combined cost of billions of dollars. It was noted that the deployment cost more than the Manhattan Project, which it was, in a way, defending against. Throughout its development there were continual questions about its real ability to deal with large attacks, and several tests by Strategic Air Command bombers suggested the system was ""leaky"". Nevertheless, SAGE was the backbone of NORADs air defence system into the 1980s, by which time the tube-based FSQ-7's were increasingly costly to maintain and completely outdated. Today the same command and control task is carried out by microcomputers, based on the same basic underlying data.