During the Cold War, the United States developed a vast nuclear arsenal with weapons on aircraft, submarines and land-based missiles. These three ways of delivering nuclear weapons became known as the triad, with the Soviet Union as the primary target.
The strategy was to deter an attack on the United States by having enough nuclear weapons that could survive a strike and retaliate.
The military commander of America’s nuclear arsenal, Admiral Cecil Haney, says this combination of nuclear arms makes it complicated for a would-be enemy to attack the United States because the forces under his command would be able to retaliate. The idea is to send the message that restraint is a better option.