Strategic Air Command (SAC), formed after World War Two, was for over forty years the main means of effecting the United States' strategy of 'containment' or deterrence of the Soviet Union in the Cold War. After 1956-7, the main SAC bomber was the B-52. The B-52 was capable of bombing the Soviet Union from bases in the United States and, in order to reduce the risk of destruction of the strategic bomber force in a pre-emptive Soviet missile strike, the B-52s were widely dispersed and a proportion was kept on standby alert, able to be airborne, fully armed and fuelled, within 15 minutes.
This proportion was supposed to be one third of the force from 1957 and a half from 1960, though there is some doubt whether these figures were actually achieved. In September 1991, President George Bush declared the Cold War over by ordering this capability to be stood down. From 1958 to 1968, a more ambitious scheme of 24 hour alert was maintained by keeping 10 to 12 aircraft airborne at any one time. During the Cuban missile crisis (1962), 70 aircraft were kept airborne for one month. After two crashes in which radioactivity was released (though the bombs did not detonate), airborne alert was suspended, never to be resumed.