Editing Semi-Automatic Ground Environment (section)

{{Short description|Historic US military computer and radar network}}
{{About|the NORAD Cold War computer network|the radar installations in each sector|SAGE radar stations}}
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| image               = Sage typical building.jpg 
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| image_caption       = The 4-story SAGE blockhouses with {{Convert|3.5|acre|ha|abbr=on}} of floor space<ref>[http://www.coldwarpeacemuseum.org/blockhouse.html The SAGE Blockhouse - Future Home of the Cold War / Peace Museum] {{webarchive|url=https://web.archive.org/web/20130511015842/http://www.coldwarpeacemuseum.org/blockhouse.html |date=2013-05-11 }}. Coldwarpeacemuseum.org. Retrieved on 2013-09-18.</ref> "were hardened [for] overpressures of" {{Convert|5|psi|abbr=on}}.{{r|Schaffel}}{{rp|264}}  A shorter adjoining building (left) had generators below the 4 intake/exhaust structures on the roof.{{r|EdwardsBenj}} (DC-01 shown) 
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| building_type       = military [[command, control, and coordination system|C<sup>3</sup>]] [[human–computer interface]]
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| opened_date         = 1958 June 26 — DC-01<br>1958 December 1 — DC-03<br>1959 (early) — CC-01<br>1966 April 1 — CC-05
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| architect           = USAF [[Air Materiel Command]]<br>[[Western Electric]]<ref name=IYD/><br>[[System Development Corporation]]<ref name=IYD/><br>[[Burroughs Corporation]]
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The '''Semi-Automatic Ground Environment''' ('''SAGE''') was a system of [[mainframe computer|large computers]] and associated [[computer network|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.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=232}}</ref> SAGE directed and controlled the [[NORAD]] response to a possible 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 after decommissioning were common props in movies such as ''[[Dr. Strangelove]]'' and [[Colossus: The Forbin Project|''Colossus'']], and on science fiction TV series such as ''[[The Time Tunnel]]''.

The processing power behind SAGE was supplied by the largest discrete component-based computer ever built, the [[AN/FSQ-7 Combat Direction Central|AN/FSQ-7]], manufactured by [[IBM]]. Each SAGE Direction Center (DC) housed an FSQ-7 which occupied an entire floor, approximately {{convert|22000|sqft|m2}} not including supporting equipment. The FSQ-7 was actually two computers, "A" side and "B" side. Computer processing was switched from "A" side to "B" side on a regular basis, allowing maintenance on the unused side. Information was fed to the DCs from a network of radar stations as well as readiness information from various defense sites. The computers, based on the raw radar data, developed "tracks" for the reported targets, and automatically calculated which defenses were within range. Operators used [[light gun (SAGE)|light gun]]s to select targets on-screen for further information, select one of the available defenses, and issue commands to attack. These commands would then be automatically sent to the defense site via [[teleprinter]].

Connecting the various sites was an enormous network of telephones, [[modem]]s and teleprinters. 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 [[autopilot]]s to maintain an intercept course without operator intervention. Each DC also forwarded data to a Combat Center (CC) for "supervision of the several sectors within the division"<ref name=Intro/> ("each combat center [had] the capability to coordinate defense for the whole nation").<ref name=Winkler/>{{Rp|<!--pdf -->51}}

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 concerns about its real ability to deal with large attacks, and the [[Operation Sky Shield]] tests showed that only about one-fourth of enemy bombers would have been intercepted.<ref name=Mola2002>{{cite news |last=Mola |first=Roger A. |url=http://www.airspacemag.com/history-of-flight/this-is-only-a-test-3119878/ |title=This Is Only a Test |work=Air & Space Magazine |date=March 2002 |access-date=26 July 2017}}</ref> Nevertheless, SAGE was the backbone of [[North American Aerospace Defense Command|NORAD]]'s air defense system into the 1980s, by which time the [[Vacuum-tube computer|tube-based]] FSQ-7s 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.