Responding to contract proposals for an interim missile launch detection system, AVCO Corporation's plan to modify existing FPS-26 height finder radars at six prime SAGE System radar sites and to install a new one near Laredo AFB, Texas was approved in July 1965. Radars were to be located at the following sites:
|SAGE ID||Location||State||Equipment||14th MWS||Notes|
|Moorestown AFS||NJ||Prototype FPS-49||Det 1|
|Z-37||Point Arena AFS||CA||Not Modified||Replaced by Mill Valley AFS|
|Z-38||Mill Valley AFS||CA||Modified FPS-26||Det 3||Replaced Point Arena AFS|
|Z-65||Charleston AFS||ME||Modified FPS-26||Det 6|
|Z-76||Mount Laguna AFS||CA||Modified FPS-26||Det 4|
|Z-l00||Mount Hebo AFS||OR||Modified FPS-26||Det 2|
|Z-115||Fort Fisher AFS||NC||Modified FPS-26||Det 5|
|Z-129||MacDill AFB||FL||Modified FPS-26||Det 7|
|Z-230||Laredo AFS||TX||New FSS-7||Det 8|
It was expected that the Avco 474N Submarine Launched Ballistic Missile (SLBM) Detection and Warning System would be operational by the end of 1967. The system included GSQ-89 data processing equipment and the modified radars were called FSS-7's. The radars provided seaward coverage of about 750 nm and with three basic modes of operation: search, acquisition, and track.
In operation, a warning and impact message was generated for transmission to the central processor at the Cheyenne Mountain 425L System Complex within 50 seconds from the initial detection of a missile. The Cheyenne Mountain Complex then relayed 474N data to SAC, the National Military Command Center (NMCC), and the Alternate NMCC over BMEWS circuits. At maximum detection range, this provided approximately 7 to 10 minutes of warning.