ABSTRACT
The concept of a "defended world" has been made the stated goal of national-security policy. In reviewing the specific critiques of a world with unconstrained defenses, it is best to remember that much of the unstated, or even unconscious, opposition to defenses is to their potential impact on classical nuclear deterrence. If both the Soviet Union and the United States have similar but limited defenses, the United States might protect more nuclear warheads in a Soviet first strike. US nuclear forces riding out the Soviet strike might be most effective against targets other than ICBMs and the other strategic operating forces. One of the most dangerous possibilities of all is a situation in which the defenses of each nation are to a significant extent vulnerable to pre-emptive attack by the other side. Technologies of defense and offense tend to develop in parallel.
