The Strategic Air Command's first intercontinental ballistic missile (ICBM) was the Convair B-65 Atlas (later redesignated SM-65). The Atlas became operational in 1959. Because of the vulnerability of the Atlas while above ground, an underground silo was developed. An elevator raised it to ground level for launching. While on alert duty, the Atlas missile was maintained in the fully raised (above ground) position since it could not be launched from its underground silo.

Credits - U.S. Air Force Museum