The network of twelve radars,[12] which was constructed beginning in 1958 and became operational in 1961, was built to detect a mass ballistic missile attack launched on northern approaches [for] 15 to 25 minutes' warning time[19] also provided Project Space Track[20] satellite data (e.g., about one-quarter of SPADATS observations).

[22] The Ballistic Missile Early Warning System (BMEWS) was a radar system built by the United States (with the cooperation of Canada and Denmark on whose territory some of the radars were sited) during the Cold War to give early warning of a Soviet intercontinental ballistic missile (ICBM) nuclear strike, to allow time for US bombers to get off the ground and land-based US ICBMs to be launched, to reduce the chances that a preemptive strike could destroy US strategic nuclear forces.

These radars provided high-resolution angular and ranging information that was fed to a computer for rapid calculation of the probable impact points of the missile warheads.

BMEWS equipment included:[23] To predict when parts might break down,[42] the contractor also installed RCA 501 computers[43] with 32k high-speed memory, 5-76KC 556 bpi 3/4" tape drives, and 200-track random-access LFE drums.

[citation needed] The initially replaced portions of BMEWS included the Ent CC&DF by the Burroughs 425L Missile Warning System at the Cheyenne Mountain Complex[44] (FOC 1 July 1966.

[45][46] On 2 June 1955, a General Electric AN/FPS-17 "XW-1" radar at Site IX[50] in Turkey that had been expedited was completed by the US in proximity to the ballistic missile launch test site at Kapustin Yar in the Soviet Union[12] for tracking Soviet rockets[49] and to demonstrate the feasibility of advanced Doppler processing, high-power system components, and computerized tracking needed for BMEWS [sic].

[12] The first missile tracked was on 15 June, and the radar's parabolic reflector was replaced in 1958,[50] and its range was extended from 1000 to 2000 nautical miles[51] after the 1957 Gaither Commission identified that because of expected Soviet ICBM development, there would be little likelihood of SAC's bombers surviving since there was no way to detect an incoming attack until the first warhead landed.

)[12] A prototype AN/FPS-43 BMEWS radar[13] completed at Trinidad in 1958 went operational on 4 February 1959, the date of an Atlas II B firing from Cape Canaveral Launch Complex 11[59] (lunar reflection was tested January–June 1960).

[48]: 158  A "satellite prediction computer" could be added to the planned missile warning center if Cheyenne Mountain's "hardened COC slipped considerably beyond January 1962"[62]: 93  (tunneling began in June 1961.)

In early 1959 for use at Ent in September 1960, a BMEWS display facility with "austere and economical construction with minimum equipment" was planned in an "annex to the current COC building".

)[76][i] The Trinidad Test Site transferred from Rome AFB to Patrick AFB on 1 July 1961 (closed as "Trinidad Air Station" on 1 October 1971)[75] and the same month, the 1st Aero began using Ent's Space Detection and Tracking System (SPADATS) operation center in building P4's annex[77] (Cheyenne Mtn's Space Defense Center became fully operational in 1967.

)[56] The BRCS undersea cable was cut "presumably by fishing trawlers" in September, October, and November 1961 (the BMEWS teletype and backup SSB substituted);[40] and in December 1961, Capt.

By 1981 Cheyenne Mountain had been averaging 6,700 messages per hour[94] compiled via sensor inputs from BMEWS, the JSS, the 416N SLBM "Detection and Warning System, COBRA DANE, and PARCS as well as SEWS and PAVE PAWS" for transmission to the NCA.