Editing Safeguard Program (section)

===Nike-X===
{{main|Nike-X}}

Faced with these problems, both the Eisenhower and Kennedy administrations turned to the newly created [[DARPA|ARPA]] to suggest solutions. ARPA noted that because the decoys were lighter than the actual warhead, they would slow down more rapidly as they reentered the lower atmosphere. They proposed a system using a short range missile that could wait until the warhead was below {{convert|100000|feet|km}} altitude, at which point the decoys would have been ''decluttered''. Desiring to destroy the missile before it was below {{convert|20000|feet|km}} altitude, combined with the {{convert|5|mile}} per second terminal speed of the RV meant there were only 2 to 3 seconds to develop a track and shoot the interceptor. This would demand extremely fast missiles, high-performance radars and advanced computers.{{citation needed|date=September 2015}}

In 1963, [[Robert McNamara]] cancelled the upcoming deployment of Zeus and announced that money would instead be provided for research into this new system, now known as Nike-X. Construction on the new [[phased array radar]] and its associated computer systems began at the MAR-I site in [[White Sands Missile Range]]. MAR could track hundreds of warheads and the interceptor missiles sent to attack them, meaning the Soviets would have to launch hundreds of missiles if they wanted to overwhelm it. And now that decoys were no longer an issue, the cost-exchange ratio fell back to reasonable levels.{{citation needed|date=September 2015}}

The Nike-X developed the same sort of trouble as the Zeus before it. In this case it was ironically due to the Soviet's own ABM system which was very similar to Zeus. To ensure they could defeat it, the [[US Air Force]] began equipping their own ICBMs with decoys, which would defeat the Soviet's Zeus-like system. However, concerned that the Soviets would upgrade their system to Nike-X like performance, they instead began replacing their warheads with lighter ones, and carrying three of them. This meant that every US missile would require three (or six accounting for redundancy) interceptors.{{citation needed|date=September 2015}}

When the same calculations were run for Nike-X, it was calculated that they would have to deploy 7,000 [[Sprint missile]]s, and the cost-exchange ratio was 20-to-1 in favor of the Soviets. When presented with these numbers, McNamara concluded that deploying Nike-X would prompt to Soviets to build more ICBMs, increasing the risk of an accidental war. From this point on, he opposed building a "heavy" ABM system like Nike-X.{{citation needed|date=September 2015}}