In an article in the October Arms Control Today, David Hoffman quotes from the declassified National Security Decision Directive 119 (NSDD-119). This Directive, issued in January 1984 by President Reagan, was the official beginning of the Strategic Defense Initiative, which was intended to develop a ballistic missile defense system.
A key reason the Directive gives for jump-starting U.S. efforts to build missile defenses is to respond to fears about possible Soviet efforts to build missile defenses. While the Reagan administration either overestimated or exaggerated Soviet efforts on missile defense, what is most interesting is the basis for the U.S. fears. NSDD-119 states that:
Unilateral Soviet acquisition of an effective defensive capability would confront the U.S. and its allies with the real threat of nuclear blackmail and political/military coercion.
Since this section of the directive remained redacted long after NSDD-119 was initially declassified, this argument appears to reflect real concerns by the administration rather than a rationale intended for public consumption.
This statement is telling for several reasons. First, it flies in the face of statements by U.S. missile defense supporters that missile defense is purely defensive so that there is no reason for other countries to be concerned about U.S. development of such a system. Even President Reagan acknowledged in 1985 the potential offensive role of the system, which lies behind the coercive role discussed in the Directive:
If someone was developing such a defensive system and going to couple it with their own nuclear weapons – yes, that could put them in a position where they might be more likely to dare a first strike.
Second, if this was a real fear U.S. leaders had at a time when the United States deployed some 14,000 strategic nuclear warheads, consider the reaction of Chinese political and military leaders to U.S. missile defense plans. They may assess the potential threat of such a system in the same way their U.S. counterparts did. China currently deploys 50 or so long-range nuclear missiles capable of hitting the United States. U.S. plans call for 30 interceptors as part of the ground-based system in Alaska and California, as well as the development over the next decade of a strategic capable sea-based interceptor designed to fit into the hundreds of Aegis launch tubes that are being called for in the coming years.