The movement toward limiting nuclear weaponry began in the mid-1960s when President Lyndon Johnson made several overtures to the Soviet Union to limit nuclear weapons. At that time the United States held a commanding four-to-one advantage in strategic nuclear weapons, and the Soviets had little interest in entering into an arms control agreement that would lock them into a position of permanent inferiority. In fact, the U.S. advantage did not last long. Soviet ICBM production steadily increased throughout the 1960s and American intelligence analysts predicted that by the end of the decade the Soviet ICBM force would equal that of the United States. The Soviets would have probably continued building more ICBMs and ignoring calls for strategic arms limitations had they not been concerned that an American breakthrough in antiballistic missile (ABM) technology could negate their efforts. Consequently, on August 19, 1968, Soviet Ambassador Anatoly Dobrynin announced that the Soviets had agreed to join in strategic arms limitation talks (SALT). Because of the change in U.S. administrations, the start of the bilateral talks was postponed until November 1969. The talks, alternating between Helsinki and Vienna, lasted for the next 30 months.
The SALT I Interim Agreement essentially froze the number of land- and sea-based launchers then in place. By the terms of the agreement the United States could keep 1,054 ICBMs and the Soviet Union 1,618. American conservatives opposed the accord, complaining that the agreement allowed the Soviets far more ICBMs than the United States. Moreover, they also pointed out that the Soviet missiles were far larger and carried more powerful warheads than U.S. ICBMs. Proponents of the agreement were quick to note that the American missiles were far more accurate, and that the Soviet edge in ICBMs was offset by the United States' three-to-one superiority in manned bombers.
On the other end of the political spectrum, U.S. liberals criticized the agreement for not going far enough. They complained that the treaty did not limit force modernization or prohibit arming missiles with multiple independently targetable reentry vehicle (MIRV) technology, which enabled a single missile to carry multiple warheads, each programmed to strike a different target. Indeed, the critics had a valid point. With no limits on the number of warheads each side could deploy, each nation's nuclear stockpile steadily increased over the coming two decades. As the leader in MIRV technology, the United States gained a strategic advantage in the early 1970s when it began equipping each Minuteman III ICBM with three MIRV warheads. However, SALT opponent Senator Henry Jackson (D-Washington) noted that in time the Soviets also would develop MIRV technology and, because their missiles were larger, they would be able to deploy even more warheads. In addition, the SALT I Interim Agreement included no provision to prevent future deployment of mobile missile 1aunchers.