The Avco 474N Submarine Launched Ballistic Missile (SLBM) Detection and Warning System (SLBMD&W System) was deployed as "an austere…interim line-of-sight system" after approval in July 1965 to modify some Air Defense Command (ADC) Avco AN/FPS-26 Frequency Diversity Radars into Avco AN/FSS-7 SLBM Detection Radars. The 474N sites planned for 1968 also were to include AN/GSQ-89 data processing equipment (for synthesizing tracks from radar returns), as well as site communications equipment that NORAD requested on 10 May 1965 to allow "dual full period dedicated data circuits" to the Cheyenne Mountain 425L System, which was "fully operational" on 20 April 1966. (Cheyenne Mountain Complex relayed 474N data to "SAC, the National Military Command Center, and the Alternate NMCC over BMEWS circuits", for presentation by Display Information Processors—impact ellipses and "threat summary display" with a count of incoming missiles and "Minutes Until First Impact" countdown).