In 1976, Lawrence Livermore Laboratory wrote MIRV: A Brief History of Minuteman and Multiple Reentry Vehicles, a document extensively detailing the development of multiple independently targetable reentry vehicles (commonly abbreviated as MIRVs) and their many reasons for being manufactured. It was publicly released in 1997.
The concept of the MIRV was officially introduced in 1962. Major advancements in rocket propulsion, guidance and target computing, alongside nuclear material weaponisation, had made it possible to build a single ballistic missile that could carry multiple nuclear warheads to destroy several targets independently. Building on from the Minuteman I missile (produced in 1960), an ICBM armed with a single nuclear warhead, the final product was the Minuteman III missile in June 1970. These ICBMs were fully operational MIRVs; the reentry vehicle itself was designated the MK-12. The first two Minuteman missiles could not be similarly equipped due to technological insufficiencies.
The advantages MIRVs gave over previous ballistic missiles were numerous. The first and most obvious advantage was the MIRV’s capacity to destroy multiple targets in a single launch, making it a highly efficient weapon.
Unlike the similar MRV (multiple reentry vehicle), which also carried several warheads, the MIRV’s superior targeting system allowed its warheads to be guided independently. This enabled them to either focus on a single target (the only option for the MRV) or on multiple areas separately, making MIRVs more versatile weapons.
As was to be expected, an individual MIRV warhead would be far less powerful than a single Minuteman I warhead (1.2 megatons); nevertheless, each warhead put out a yield of 170 kilotons, making them over eight times more powerful than the Hiroshima bomb.
However, the chief reason why the U.S. developed the MIRV at all was in response to the Soviet Union and its advancements in anti-ballistic missile (ABM) technology, a threat that became apparent by 1960.
With a fully operational ABM defence programme, the Soviets could potentially destroy any incoming enemy missile before it ever reached its intended target. For this reason, the Minuteman I had become redundant against the Soviet Union’s ABMs. Without an effective deterrent, the U.S. superpower status would be jeopardised. The MIRV was a brilliantly simple solution to ABMs; with multiple warheads being launched from a single missile, any ABM system would be inundated, enabling some of the warheads to penetrate the defence and destroy their intended targets.
The U.S. sought a diplomatic solution in the ABM Treaty in 1972 rather than build their own ABM programme; nonetheless, they realised that equipping their missiles with MIRVs was far more cost-effective. With fewer missiles carrying more warheads, money didn’t need to be spent on constructing more missile silos and launchers. Consequentially, the MIRV was a very economical investment, such that even though military spending decreased over the era of détente, both sides increased the potency of their regulated arsenals through MIRVs.
Throughout the Strategic Arms Limitation Talks (SALT), the ideal objective was to minimise the number of ICBMs and ABMs on both sides to promote détente. In reality however, both the U.S. and the Soviet Union shared the same ulterior motive; to lower the number of weapons on the other side first and to negotiate mutual reduction only as a final resort. This sheds a rather cynical light on the motives behind détente and SALT; neither side was actually interested in tethering the arms race as a whole. Even under SALT’s self-imposed restrictions, the U.S. was determined to remain ahead in the arms race.
For this reason, MIRVs were ideal for this era; it allowed the U.S. to have fewer missiles, while at the same time increasing their nuclear stockpile. For a time, the MIRV was the U.S.’s loophole in maintaining the balance of power under SALT.
Naturally, as SALT progressed, MIRVs became a heated topic for discussion. In 1973, the U.S. sought to prohibit MIRV-equipped heavy ICBMs testing. This was doubtlessly because they already had an operational MIRV program; the proposal was an attempt to retard the Soviet’s development of MIRVs. The Soviet Union rejected this, as they were eager to replicate MIRV technology, which they did by 1976.
In 1977, in the emergence of SALT II, now that both sides had MIRVs, both endeavoured to limit their numbers, to which there was some agreement. President Carter unsuccessfully proposed limits to six test-firings per year, which would have severely hindered the Soviets in properly testing the accuracy and effectiveness of any new MIRV weaponry.
Although MIRVs emerged during the era of détente, it has been acknowledged to some extent that even though on the surface, the 1970s was seen as the period of relaxation and negotiation between the world’s superpowers, the arms race was still being continued. Paradoxically, in the bid to negotiate limits on apocalyptic weaponry, the U.S. and the Soviet Union emerged with far deadlier arsenals than before they entered SALT. MIRVs, by and large, had made this possible.