Multiple Independently Targetable Reentry Vehicles (MIRVs)

Vehicles mounted on a ballistic missile and containing several nuclear warheads, each of which may be programmed to strike a separate target. The multiple independently targetable reentry vehicle (MIRV) was developed to enhance first-strike capability of nuclear warheads by increasing the number of targets a single missile could strike. The MIRV is one of a number of nuclear weapons that can be transported by an intercontinental ballistic missile (ICBM) or a submarine-launched ballistic missile (SLBM).

The MIRV is distinct from the multiple reentry vehicle (MRV), which deploys multiple warheads against a single target. Because both MRVs and MIRVs can strike several different targets, they are more attractive to advanced nuclear powers such as the United States and Russia. Nations with less-advanced nuclear technology, such as India or Pakistan, prefer single warhead missiles because of the large amount of nuclear material consumed by multiple warhead missiles. In the U.S. nuclear arsenal, the Polaris sea-launched ballistic missile is an example of an MRV. The sea-launched Poseidon and Trident, and the land-based Minuteman and Peace Keeper, are MIRVs.

The idea for the MIRV dates to the early 1960s. A necessary condition for the deployment of MRVs was the creation of small thermonuclear weapons. The positioning of multiple space satellites at various orbits to direct the missiles was also essential. Both of these technological advances were accomplished by 1962, and the conception and design of multiple, separately targeted warheads could begin. Meanwhile, advances on Minuteman missile technology and the development of increased pay-loads allowed for an increase in the size of the weapons package and supporting equipment carried by ICBMs. This had taken place by the latter half of the 1960s.

The development of MIRVs coincided with the development of a national missile defense system in the United States. U.S. military planners assumed that the Soviet Union would try to deploy a similar defensive system. An important purpose of the MIRV was to circumvent antiballistic missile (ABM) systems that relied on intercepting individual warheads. Intercepting missiles would have only one warhead, whereas the MIRV would have anywhere from three to twelve. This would also increase the cost of any Soviet antimissile system.

The designers of the MIRV envisioned several important advantages over standard nuclear warheads. One advantage was the reduction of collateral damage. Aimed at enemy missile silos or bases, MIRVs could pinpoint targets so accurately that larger or more devastating warheads were unnecessary. Another advantage of the MIRV was that it reduced the number of missiles need to carry out a successful attack. Rather than launching several missiles, one missile could be launched to strike a number of targets across a vast geographic area, if desired.

Like other weapons systems, both offensive and defensive, the MIRV was also promoted for its peace-keeping capabilities. Proponents argued that it would serve to maintain the balance of power between the United States and the Soviet Union. However, the fact that the MIRV increased both U.S. first-strike capability and its response capability likely sped the momentum of the arms race rather than slowed it.

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