Sentinel program

Sentinel was a proposed US Army anti-ballistic missile (ABM) system designed to provide a light layer of protection over the entire United States, able to defend against small ICBM strikes like those expected from China, or accidental launches from the USSR or other states. The system would have seventeen bases, each centered on its Missile Site Radar (MSR) and a computerized command center buried below it. The system was supported by a string of five long-range Perimeter Acquisition Radars (PAR) spread across the US/Canada border area and another in Alaska. The primary weapon was the long-range Spartan missile, with short range Sprint missiles providing additional protection near US ICBM fields and PAR sites. The system would initially have a total of 480 Spartan and 192 Sprint missiles.
Sentinel was a response to the rapidly rising costs of the earlier Nike-X concept. Nike-X was designed to handle full-out attacks by the Soviet ICBM force of thousands of missiles, stockpiling more interceptors than the Soviets had ICBMs. As the number of Soviet ICBMs grew, the number of interceptor missiles required to maintain the defense soared. Calculations suggested it would cost twenty times...