Sprint (missile)

The Sprint was a two-stage, solid-fuel anti-ballistic missile that Martin Marietta developed for the United States Army, armed with a W66 enhanced-radiation thermonuclear warhead. It was built to intercept incoming reentry vehicles after they had dropped below about 60 kilometres, where the thickening air exposed them to radar. To do that it accelerated at 100 g and reached Mach 10 in five seconds, which heated its skin enough to need an ablative shield and wrapped the missile in a plasma that made radio guidance difficult. Sprint was the close-in layer of the Nike-X, Sentinel and Safeguard missile defence plans, working beside the longer-ranged LIM-49 Spartan. Safeguard was operational for only a few months from October 1975 to early 1976, so Sprint served in 1975 and 1976. Some work on an improved Sprint II, mostly on guidance, was done in the early 1970s before United States anti-ballistic missile policy changed and it stopped.