The strategic nuclear forces of the two nations were changing in character in the late 1960s. The Soviet program was for the continued deployment of heavy land-based missiles and new ballistic missile submarines; the Soviet Union was deploying around 200 more missiles every year from around 1968. The US total number of missiles had been static since 1967 at 1,054 ICBMs and 656 SLBMs but there was a increasing number of missiles with MIRV warheads being deployed. Both nations were developing anti-ballistic missile (ABM) systems, the Soviet Union deploying such a system around Moscow in 1966 and the United States announcing an ABM program to protect twelve ICBM sites in 1967.
Negotiations lasted from November 1969 until May 1972 in a series of meetings beginning in Helsinki on November 17, 1969. Further sessions alternated between Vienna and Helsiniki. After a long deadlock the first results of SALT I was in May 1971 when agreement was reached over anti-ballistic missile systems. Further discussion brought the negotiations to an end on May 26, 1972 in Moscow when Richard Nixon and Leonid Brezhnev signed the Anti-Ballistic Missile Treaty and the Interim Agreement Between The United States of America and The Union of Soviet Socialist Republics on Certain Measures With Respect to the Limitation of Strategic Offensive Arms (see SALT I treaty). A number of agreed statements were also made.