The military purpose of a MIRV is fourfold: • Enhance
first-strike proficiency for strategic forces. • Providing greater target damage for a given
thermonuclear weapon payload. Several small and lower yield 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. • 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 attacking MIRV missile can have multiple warheads (312 on United States and Russian missiles), 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
re-entry 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 their first-strike capability that land-based MIRVs were banned under the
START II agreement. START II was ratified by the
Russian Duma on 14 April 2000, but Russia withdrew from the treaty in 2002 after the US withdrew from the
ABM treaty. == Operation ==