A model of defense-protected build-down.

In a process of defense-protected build-down (DPB), each of the two nuclear superpowers begins by deploying a significant increase in the effectiveness of its defenses against an attack on its own strategic missiles. This is followed by a sequence of alternating reductions in strategic missile forces by the two sides. At each step of the process, each side maintains a desired "level of deterrence" (this term will be defined precisely). For the side that initiates the DPB, the initial increase in the effectiveness of defense makes possible a corresponding reduction in its missile forces while maintaining the desired level of deterrence. Thus the DPB can be initiated unilaterally, without any increase in vulnerability.