A 107½-ton, 4½-foot-thick, wedge-shaped launcher closure door protected a nuclear-tipped Minuteman missile a few feet below it between 1966 and 1997. The door was designed to be heavy and thick enough to prevent enemies from moving or penetrating it and accessing the missile or its nuclear warheads, while also helping the missile survive a nearby nuclear blast. At the same time, it could not be so heavy, large, or immovable that it could not be opened when needed for maintenance or launch. Missile maintainers used a temporary pipe pusher, which worked with a cogged rail between two smooth rails and the door's four 18-inch wheels, to hydraulically roll the massive door open or closed for access to the warheads and guidance computer. In a launch, however, that method was too slow, so engineers placed ballistic gas actuators beneath and behind the door. When a missile crew commanded launch, the actuators fired and accelerated the 107 1/2-ton blast door to an almost instantaneous speed of 35 mph, while its wedge-shaped leading edge cleared debris from its path.