nuclear triad, a three-sided military-force structure consisting of land-launched nuclear missiles, nuclear-missile-armed submarines, and strategic aircraft with nuclear bombs and missiles. The triad was a central element of the U.S. military strategy (and, to a lesser degree, that of the Soviet Union) during the Cold War, with its concomitant arms race. The theory underlying the triad was that spreading the assets comprising the country’s extensive nuclear arsenal across various weapons platforms would make the force more likely to survive an attack by the Soviet Union and to be able to respond to a first strike successfully.

The political and military strategy of distributing nuclear weapons resources over the three platforms developed as an answer to each country’s concerns with surviving a first strike by the other and with ensuring that sufficient nuclear forces survived to conduct a second strike, resulting in “mutually assured destruction.” For example, the land component of the U.S. triad included ICBMs (intercontinental ballistic missiles) ranging from the Atlas to the Titan to the Minuteman and, later, to the Peacemaker missile, all of which were multistage rockets capable of carrying one or more nuclear weapons and guided by highly developed inertial guidance systems. With a range of 8,000 km (5,000 miles) or more, those missiles posed a formidable threat to an enemy. The sea-based component of the triad included older nuclear-powered submarines as well as more modern Trident submarines carrying sea-launched missiles such as Poseidon C-3s and Trident C-4s. The air component of the triad included bombers such as the B-52 and B-1B bombers, equipped with eight or more nuclear bombs. After the end of the Cold War, the triad continued to be a component of U.S. military strategy, but with reduced nuclear arsenals and inventories.