The Strategic Air Command (SAC) was both a major command and a "specified command" in the U.S. Air Force and was the operational establishment in charge of America's land-based bomber aircraft and land-based ballistic missile strategic nuclear arsenal from 1946-92. SAC also controlled the infrastructure necessary to support the strategic bomber and ICBM operations, such as tanker aircraft to refuel the bombers in flight, strategic reconnaissance and command post aircraft, and, until 1957, fighter escorts. Following the fall of the Soviet Union, SAC was succeeded in June 1992 by the U.S. Strategic Command.