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A multiple independently targetable reentry vehicle (MIRV) is a ballistic missile payload containing several warheads, each capable of being aimed to hit one of a group of targets. By contrast a unitary warhead is a single warhead on a single missile. An intermediate case is the multiple reentry vehicle (MRV) missile which carries several warheads which are dispersed but not individually aimed. Britain, China, France, Russia and the United States are known to possess MIRV missiles. == Purpose == The military purpose of a MIRV is fourfold: *Enhance first strike proficiency for strategic forces.〔(【引用サイトリンク】url=http://www2.gwu.edu/~nsarchiv/nsa/NC/mirv/mirv.html )〕 *Providing greater target damage for a given thermonuclear weapon payload. Several small warheads cause much more target damage area than a single warhead alone. This in turn reduces the number of missiles and launch facilities required for a given destruction level - much the same as the purpose of a cluster munition.〔The best overall printed sources on nuclear weapons design are: Hansen, Chuck. ''U.S. Nuclear Weapons: The Secret History.'' San Antonio, TX: Aerofax, 1988; and the more-updated Hansen, Chuck, "(Swords of Armageddon: U.S. Nuclear Weapons Development since 1945 )" (CD-ROM & download available). PDF. 2,600 pages, Sunnyvale, California, Chukelea Publications, 1995, 2007. ISBN 978-0-9791915-0-3 (2nd Ed.)〕 *With single warhead missiles, one missile must be launched for each target. By contrast with a MIRV warhead, the post-boost (or bus) stage can dispense the warheads against multiple targets across a broad area. *Reduces the effectiveness of an anti-ballistic missile system that relies on intercepting individual warheads. While a MIRV attacking missile can have multiple warheads (3–12 on United States missiles and 3-12 on Russian), interceptors may have only one warhead per missile. Thus, in both a military and an economic sense, MIRVs render ABM systems less effective, as the costs of maintaining a workable defense against MIRVs would greatly increase, requiring multiple defensive missiles for each offensive one. Decoy reentry vehicles can be used alongside actual warheads to minimize the chances of the actual warheads being intercepted before they reach their targets. A system that destroys the missile earlier in its trajectory (before MIRV separation) is not affected by this but is more difficult, and thus more expensive to implement. MIRV land-based ICBMs were considered destabilizing because they tended to put a premium on striking first. The world's first MIRV—US Minuteman III missile of 1970—threatened to rapidly increase the US's deployable nuclear arsenal and thus the possibility that it would have enough bombs to destroy virtually all of the Soviet Union's nuclear weapons and negate any significant retaliation. Later on the US feared the Soviet's MIRVs because Soviet missiles had a greater throw-weight and could thus put more warheads on each missile than the US could. For example, the US MIRVs might have increased their warhead per missile count by a factor of 6 while the Soviets increased theirs by a factor of 10. Furthermore, the US had a much smaller proportion of its nuclear arsenal in ICBMs than the Soviets. Bombers could not be outfitted with MIRVs so their capacity would not be multiplied. Thus the US did not seem to have as much potential for MIRV usage as the Soviets. However, the US had a larger number of Submarine-launched ballistic missiles, which could be outfitted with MIRVs, and helped offset the ICBM disadvantage. It is because of this that this type of weapon was banned under the START II agreement. However, START II was never ratified by the Russian Duma due to disagreements about the ABM treaty. 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「multiple independently targetable reentry vehicle」の詳細全文を読む スポンサード リンク
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