SALT — the Strategic Arms Limitation Talks — produced two agreements between the United States and the Soviet Union. SALT I, signed in Moscow on May 26, 1972, consisted of the ABM Treaty and the Interim Agreement on Offensive Arms, both of which were ratified and entered into force. SALT II, signed in Vienna on June 18, 1979, set numerical ceilings on strategic delivery vehicles and MIRVed warheads, but was never ratified by the U.S. Senate — withdrawn from consideration in January 1980 after the Soviet invasion of Afghanistan. The framework the talks established, however, became the technical basis for START I in 1991.
Both agreements were designed to slow, not reverse, the nuclear buildup. Neither mandated cuts. See the SALT treaties and arms control for the full negotiation history.
The SALT I package contained two documents. The Anti-Ballistic Missile (ABM) Treaty limited each side to two ABM deployment areas, reduced to one by a 1974 protocol. The Interim Agreement froze the number of ICBM and SLBM launchers at existing levels. It did not address warheads, bombers, or MIRVs, and was explicitly temporary. The package was negotiated in Helsinki and Vienna by Gerard Smith and Vladimir Semenov, and signed at the Moscow Summit of May 1972.
SALT II was an attempt to address what SALT I had deferred. The agreement set a ceiling of 2,400 strategic nuclear delivery vehicles per side, of which 1,320 could be MIRVed, with sub-ceilings on MIRVed ICBMs, MIRVed SLBMs, heavy ICBMs, and throw-weight. The treaty included detailed counting rules and the continuation of the Standing Consultative Commission. It was signed in Vienna on June 18, 1979. The Soviet invasion of Afghanistan in December 1979 led Carter to withdraw it from Senate consideration in January 1980. The SALT II limits were observed on a voluntary basis by both sides through 1986.
SALT did not reduce the number of nuclear weapons — warhead counts grew through the 1970s, mainly through MIRVing existing launchers. SALT did, however, slow the rate of growth, impose predictability on a previously open-ended competition, and establish the verification architecture that subsequent agreements built on.