warheads would be moving at about at this point, they were only seconds from their targets. An extremely high-speed missile would be needed to attack them during this period. Sprint The result of the ARPA study came at the height of the debate over the Zeus system in the early 1960s. The new Secretary of Defense, Robert McNamara, convinced President Kennedy that Zeus was simply not worth deploying. He suggested using the funds allocated to its deployment to develop the ARPA system, which became known as Nike-X, a name given by engineering professor Jack Ruina when he was reporting on the concept. Nike-X required great improvements in radars, computers, and especially the missile. Zeus had an attack profile lasting about a minute; Nike-X's interceptions would last about five seconds. Sprint II Work on initial investigations into "Follow-On Sprint" was underway in second-quarter 1968. Los Alamos were examining two warheads for the Upstage II design variation. By third-quarter 1971, Sprint II was incorporated into a new module for Safeguard called Hardsite Defense (HSD) and a joint Atomic Energy Commission/DoD working group was examining new warheads that would require less tritium. HSD was described as: By first-quarter 1972, the system was renamed Site Defense and its purpose was to defend Minuteman Silos. Over the original Sprint missile, the Sprint II interceptor had slightly reduced launch dispersion, increased hardness to the effect of nuclear weapons, and decreased miss distance. Los Alamos staff expected a request for warhead development sometime in FY-1972-1974. A Phase 2 feasibility study report was completed by Los Alamos in third-quarter 1972 and investigations into warhead design continued into first-quarter 1973. It is unclear when Sprint II was cancelled, however a report on Sprint II electrical connectors was published in April 1977. Design The conical Sprint was stored in and launched from a silo. To make the launch as quick as possible, the cover was blown off the silo by explosive charges; then the missile was ejected by an explosive-driven piston. As the missile cleared the silo, the first stage fired and the missile was tilted toward its target. The first stage was exhausted after only 1.2 seconds, but produced of thrust. On separation, the spent first stage disintegrated due to aerodynamic forces. The second stage fired within 1 to 2 seconds of launch. Interception at an altitude of took at most 15 seconds. The first stage's Hercules X-265 engine