In nuclear warfare, enemy targets are divided into two types; a counterforce target is an element of the military infrastructure, usually either specific weapons or the bases which support them. A counterforce strike is an attack which targets these elements whilst leaving the civilian infrastructure – known as countervalue targets – as undamaged as possible.
An ideal counterforce attack would kill no civilians. Military attacks are prone to causing collateral damage however, and this is especially true when nuclear weapons are employed. In nuclear terms many military targets are located in proximity to civilian centres, and a major counterforce strike employing even relatively small nuclear warheads against a nation like the United States of America would undoubtedly inflict millions of civilian casualties.
Counterforce is a type of attack which was originally proposed during the Cold War.
Both sides in the Cold War took steps to protect at least some of their nuclear forces from counter-force attacks. At one point the US kept B-52 Stratofortress bombers permanently in flight; these would remain operational after any counter-force strike. Other bombers were kept ready for launch on short notice, allowing them to escape their bases before intercontinental ballistic missiles could destroy them. The deployment of nuclear weapons on ballistic missile submarines changed this equation considerably – submarines launching from positions off the coast would likely destroy airfields before bombers could launch, reducing their ability to survive an attack. Submarines themselves, however, are largely immune from counter-force strikes and both sides fielded many such weapons during the Cold War.
A counter-force exchange was one scenario mooted for a possible limited nuclear war. The concept was that one side might launch a counter-force strike against the other; the victim would recognize the limited nature of the attack and respond in kind, leaving the military capability of both sides largely destroyed. The war might then come to an end because both sides would recognize that any further action would lead to attacks on the civilian population from the remaining nuclear forces – a counter-value strike. Critics of this idea claimed that since even a counter-force strike would kill millions of civilians it is unlikely that escalation to a full-scale counter-value war could be prevented.
MIRVed land-based ICBMs are considered destabilizing because they tend to put a premium on striking first. If, for example, each side has 100 missiles, with 5 warheads each, and further that each side has a 95 percent chance of neutralizing the opponent's missiles in their silos by firing 2 warheads at each silo. In this case, the side that strikes first can reduce the enemy ICBM force from 100 missiles to about 5 by firing 40 missiles with 200 warheads, and keeping the rest of 60 missiles in reserve. For such an attack to be successful, the warheads would have to strike their targets prior to the enemy launching a counter-attack. It is because of this that this type of weapon was banned under the START II agreement.