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The Anti-Ballistic Missile Treaty (ABM Treaty or ABMT) was a treaty between the United States and the Soviet Union on the limitation of the anti-ballistic missile (ABM) systems used in defending areas against ballistic missile-delivered nuclear weapons. Under the terms of the treaty, each party was limited to two ABM complexes, each of which was to be limited to 100 anti-ballistic missiles. Signed in 1972, it was in force for the next 30 years. Following the dissolution of the Soviet Union, in 1997 the United States and four former Soviet republics agreed to succeed to the treaty. In June 2002 the United States withdrew from the treaty, leading to its termination. ==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 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 1950s, 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Anti-Ballistic Missile Treaty」の詳細全文を読む スポンサード リンク
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