Ballistic-missile defense has been continuously researched in the United States for the past 14 years. The Safeguard system itself is an outgrowth of both the Nike?Zeus system and later ballistic-missile components developed by various government agencies. The classic result of this early work was clear?an ICBM could be intercepted by another missile. Hence, the real controversy concerning the workability of such systems centered around an entirely different problem?the ``high-traffic environment''?or how to make tens to hundreds of near-simultaneous intercepts while tracking thousands of targets. This article describes the radars that have led to a solution of this problem, and how such radars operate within the framework of the world's most sophisticated defense system.