The United States has been developing missile defense technologies since the beginning of the Cold War, first with nuclear-tipped interceptors and later with conventional so-called "hit-to-kill" missiles--weapons intended to destroy enemy warheads in flight. As of 2009, the U.S. Missile Defense Agency was testing and maintaining over a dozen interconnected sensors, radars, command-and-control systems, and missile silos. But development has not been without controversy, as this Backgrounder explains. While the Pentagon maintains its testing and deployment schedules are effective, critics argue testing relies on unrealistic battle conditions that would easily be defeated by North Korea, Iran, or other potential adversaries. What follows is an overview of current and planned technologies that make up the program, collectively known as the Ballistic Missile Defense System (BMDS).
Ground-Based Midcourse Defense (GMD): The most complex and costly component of the U.S. government's missile defense system, the GMD, is designed to counter long-range intercontinental ballistic missiles that threaten U.S. territories, deployed forces, and allies. It seeks to detect, track, and destroy missiles in flight by launching a ground-based interceptor missile which releases into space a smaller projectile--the "Exo-atmospheric Kill Vehicle." Once released, the kill vehicle would track and collide with the enemy missile. Currently, twenty-four interceptors are positioned in silos at Fort Greely, Alaska, and Vandenberg Air Force Base, California. The Pentagon has planned for a total of forty-four by 2011, with ten additional interceptor missiles charted for deployment in Poland. A series of interconnected radar systems are also positioned around the world, including in Japan and Britain, to communicate with the kill vehicles while in flight. But hardware problems associated with the kill vehicles halted a pair of planned tests in 2008, raising doubts about the GMD's overall functionality. In total, six of the system's fourteen...