Atlas D (SM-65D)

Atlas D (SM-65D) was the first operational model of the United States Atlas intercontinental ballistic missile and the direct basis for several early American space boosters. Its pressure-stabilized stainless-steel airframe used a stage-and-a-half propulsion arrangement; retired missiles and D-series hardware supported Mercury, reentry-vehicle research, and Orbiting Vehicle 1 missions after the weapon left alert service.