Throughout the Cold War, as the nuclear arms race became more frantic, a nuclear confrontation between the U.S. and the Soviet Union remained a major concern.

With intercontinental ballistic missiles, submarine-launched missiles, and air-dropped bombs, both countries had several options when it came to nuclear warfare.

But the atomic bombings of Hiroshima and Nagasaki in the closing days of World War II made clear the destructive capability of nuclear arms and the danger of a full-blown nuclear conflict.

As a result, U.S. strategists sought ways to use nuclear weapons without triggering an all-out nuclear war.