ABM

A particular concern was the development of anti-ballistic missile, or ABM, defences. These were designed to shoot down incoming missiles. Although apparently defensive, they could make the nuclear balance less stable: a government might believe that it could attack first and then use its defences to block retaliation.

An anti-ballistic missile, or ABM, was designed to shoot down an incoming missile. This sounds purely defensive, but an effective defence system could destabilise the nuclear balance. A leader might believe that their country could launch a first strike and then intercept the enemy’s surviving missiles.