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.

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, and on science fiction TV series such as The Time Tunnel.

Each SAGE Direction Center (DC) housed an FSQ-7 which occupied an entire floor, approximately 22,000 square feet (2,000 m2) not including supporting equipment.

The computers, based on the raw radar data, developed "tracks" for the reported targets, and automatically calculated which defenses were within range.

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.

By 1944, analog computers had been installed at the CH stations to automatically convert radar readings into map locations, eliminating two people.

Meanwhile, the Royal Navy began experimenting with the Comprehensive Display System (CDS), another analog computer that took X and Y locations from a map and automatically generated tracks from repeated inputs.

A similar system was also specified for the Nike SAM project, specifically referring to a US version of CDS,[9] coordinating the defense over a battle area so that multiple batteries did not fire on a single target.

[10] A system tasked with defending cities against the predicted future Soviet bomber fleet would have to be dramatically more powerful than the models used in the NTDS or DATAR.

In September 1950, an early microwave early-warning radar system at Hanscom Field was connected to Whirlwind using a custom interface developed by Forrester's team.

[10] With this successful demonstration, Louis Ridenour, chief scientist of the Air Force, wrote a memo stating "It is now apparent that the experimental work necessary to develop, test, and evaluate the systems proposals made by ADSEC will require a substantial amount of laboratory and field effort.

"[10] Ridenour approached MIT President James Killian with the aim of beginning a development lab similar to the war-era Radiation Laboratory that made enormous progress in radar technology.

[14] Project Charles was placed under the direction of Francis Wheeler Loomis and included 28 scientists, about half of whom were already associated with MIT.

[citation needed] In a test for the US military at Bedford, Massachusetts on 20 April 1951, data produced by a radar was transmitted through telephone lines to a computer for the first time, showing the detection of a mock enemy aircraft.

[21]: 128  The USAF had decided by April 10, 1953, to cancel the competing ADIS (based on CDS), and the University of Michigan's Aeronautical Research Center withdrew in the spring.

[2]: 223  "On 31 December 1958, USAF ADC had 187 operational land-based radar stations" (74 were "P-sites", 29 "M-sites", 13 "SM-sites", & 68 "ZI Gap Fillers").

The concept of the system, according to the Lincoln Laboratory site was to "develop a digital computer that could receive vast quantities of data from multiple radars and perform real-time processing to produce targeting information for intercepting aircraft and missiles.

It has been suggested the FSQ-7 was based on the IBM 701 but, while the 701 was investigated by MIT engineers, its design was ultimately rejected due to high error rates and generally being "inadequate to the task.

[33] For SAGE consulting Western Electric and Bell Telephone Laboratories formed the Air Defense Engineering Service (ADES),[34] which was contracted in January 1954.

[2]: 197  Initially contracted to RCA, the AN/FSQ-7 production units were started by IBM in 1958[citation needed] (32 DCs were planned[2]: 207  for networking NORAD regions.

General Operational Requirements (GOR) 79 and 97 were "the basic USAF documents guiding development and improvement of [the semi-automatic] ground environment.

The plan identified deactivation of the Eastern, Central, and Western Region/Defense Forces on July 1, 1960, and "current manual boundaries" were to be moved to the new "eight SAGE divisions" (1 in Canada, "the 35th") as soon as possible.

[46] By the middle of 1960, AMC had determined that about 800,000 man-hours (involving 130 changes) would be required to bring the F-106 fleet to the point where it would be a valuable adjunct to the air defense system.

")[25] Construction of CFB North Bay in Canada was started in 1959 for a bunker ~700 feet (210 m) underground (operational October 1, 1963),[52] and by 1963 the system had 3 Combat Centers.

; and AT&T's "main underground station" was in Kansas (Fairview) with other bunkers in Connecticut (Cheshire), California (Santa Rosa), Iowa (Boone)[75] and Maryland (Hearthstone Mountain).

NORAD Division Warning Networks) provided the radar netting communications for each DC[26] and eventually also allowed transfer of command guidance to autopilots of TDDL-equipped interceptors for vectoring to targets[43] via the Ground to Air Data Link Subsystem and the Ground Air Transmit Receive (GATR) network of radio sites for "HF/VHF/UHF voice & TDDL"[73] each generally co-located at a CDTS site.

[citation needed] The ADL was designed to allow Interceptors that reached targets to transmit real-time tactical friendly and enemy movements and to determine whether sector defence reinforcement was necessary.

the AN/FST-2,[76] and sectors without AN/FSQ-7 centrals requiring a "weapon direction control device" for USAF air defense used the solid-state AN/GSG-5 CCCS instead of the AN/GPA-73 recommended by ADC in June 1958.

Back-Up Interceptor Control (BUIC)[26] with CCCS dispersed to radar stations for survivability allowed a diminished but functional SAGE capability.

[3] Company histories identifying employees' roles in SAGE include the 1981 System Builders: The Story of SDC[96] and the 1998 Architects of Information Advantage: The MITRE Corporation Since 1958.