The Minuteman III is a solid-fueled, intercontinental ballistic missile (ICBM), which the U.S. Air Force first deployed in the 1960s. The guidance system, contained in a ring between the upper stage and the re-entry vehicle, was a key to the Minuteman's success as a weapon. Signals from this system controlled the direction, cut-off of thrust, and the separation of the stages, to direct the three warheads to their targets.The Minuteman used an inertial guidance system, which relied completely on internal measurements of acceleration. By combining acceleration data with knowledge of the Earth's gravitational field, and of the missile's exact position at launch, the Minuteman was able to achieve remarkable accuracy. An onboard digital computer, built of early production integrated circuits, stored data and performed the necessary calculations. It also allowed the missile to be retargeted quickly prior to launch.Transferred by the U.S. Air Force to the Museum in 1977.