The Triad Doctrine
The Triad Doctrine resulted from conceptual differentiation of Flexible Response. The Triad Doctrine distinguishes a strategic triad: Inter-continental Ballistic Missiles (ICBMs), Submarine Launched Ballistic Missiles (SLBMs), and strategic bombers. The idea of the Triad Doctrine was that each should be able independently to impose unacceptable damage on the Soviet Union. If two legs were destroyed the third could retaliate.
Strategic bombers were vulnerable unless air-borne, but they can be recalled. ICBMs were more