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Anti-Ballistic Missile Treaty

1972 arms control treaty between the United States and the Soviet Union

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Under the terms of the original 1972 treaty, each party was limited to two ABM complexes, one for the nation's capital and one for an intercontinental ballistic missile silo field. Each ABM complex was limited to 100 anti-ballistic missiles and their launchers, two phased-array radars, and 18 smaller radars for early-warning. ABM missiles that were not static and ground-based were prohibited. In 1974, the limit was reduced to just a single ABM complex. The USSR chose to deploy the A-35 system around its capital Moscow, the US elected to deploy the Safeguard Complex around its ICBM fields of the Twentieth Air Force, although this was only operational for a year from 1974 to 1975. A 1997 treaty addendum permitted "theater missile defense": anti-ballistic missiles used against theatre ballistic missiles, as long as they were not tested against targets with velocities over 5 km/s, typical of ICBM terminal phase. Also in 1997, five years after the dissolution of the Soviet Union, its former member states Belarus, Kazakhstan, Russia, and Ukraine were established as successors to the USSR within the treaty, with one ABM system permitted between them.

Background

Throughout the late 1950s and into the 1960s, the United States and the Soviet Union had been developing missile systems with the ability to shoot down incoming Intercontinental ballistic missile (ICBM) warheads. During this period, the US considered the defense of the US as part of reducing the overall damage inflicted in a full nuclear exchange. As part of this defense, Canada and the US established the North American Air Defense Command (now called North American Aerospace Defense Command).

By the early 1960s, US research on the Nike Zeus missile system had developed to the point where small improvements would allow it to be used as the basis of an operational ABM system. Work started on a short-range, high-speed counterpart known as Sprint to provide defense for the ABM sites themselves. By the mid-1960s, both systems showed enough promise to start development of base selection for a limited ABM system dubbed Sentinel. In 1967, the US announced that Sentinel itself would be scaled down to the smaller and less expensive Safeguard. Soviet doctrine called for development of its own ABM system and return to strategic parity with the US. This was achieved with the operational deployment of the A-35 ABM system and its successors, which remain operational to this day.

The development of multiple independently targetable reentry vehicle (MIRV) systems allowed a single ICBM to deliver as many as ten separate warheads at a time. An ABM defense system could be overwhelmed with the sheer number of warheads. Upgrading it to counter the additional warheads would be economically unfeasible: The defenders required one rocket per incoming warhead, whereas the attackers could place 10 warheads on a single missile at a reasonable cost. To further protect against ABM systems, the Soviet MIRV missiles were equipped with decoys; R-36M heavy missiles carried as many as 40. These decoys would appear as warheads to an ABM, effectively requiring engagement of five times as many targets and rendering defense even less effective.

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