Multiple independently targetable reentry vehiclenuclear 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 configuration of the Minuteman III. (Not allowed under START-2).
The military purpose of a MIRV is twofold.
- To reduce or eliminate the effectiveness of an anti-ballistic missile system that relies on intercepting individual warheads. While a MIRVed attacking missile can have multiple (3-12 on various US missiles) warheads, interceptors can only have one warhead per missile. Thus, in both a military and practical sense, MIRVs render ABM systems less effective, as the costs of maintaining a workable defense against MIRVs would grow astronomically, and would require multiple defensive missiles for each offensive one.
- To reduce the number of missiles required to carry out an attack. With single warhead missiles, one missile must be launched for each target. The post-boost stage (or bus) of a MIRV can dispense the warheads against multiple targets across a broad area.