Multiple independently targetable reentry vehicle

A multiple independently targetable re-entry vehicle, or MIRV, is one of a collection of nuclear weapons carried on a single intercontinental ballistic missile (ICBM) or a submarine launched ballistic missile (SLBM). Using MIRVs, a single launched missile can strike several targets, or fewer targets redundantly. the image below shows three W-78/Mk-12A re-entry vehicles on a Rocketdyne RS-14 post-boost stage, the standard minuteman III's configuration (Not allowed under START-2).

The military purpose of a MIRV is to reduce or eliminate the effectiveness of an anti-ballistic missile system. While a MIRVed attacking missile can have from three to ten warheads, interceptors can only have one warhead per missile. Thus, in both a military and practical sense, MIRVs render ABM systems ineffective and inefficient, as the costs of maintaining a workable defense against MIRVs would grow astronomically, and would require three to ten defense missiles for each offensive one. The most powerful MIRV developed by the USA was the Peacekeeper missile, which could carry up to 10 cone-shaped re-entry vehicles, each of which with a maximum explosive power of 300 kilotons.

See also Multiple Reentry vehicle, Poseidon missile, Trident missile.