The term “national missile defense” (NMD) has a variety of connotations. It is, first and foremost, the concept of a country’s comprehensive missile defense system to protect it from incoming missiles, particularly nuclear-tipped intercontinental ballistic missiles (ICBMs). The term was once used to refer to the United States’ National Missile Defense system, which was renamed Ground-Based Midcourse Defense in 2002. It now most commonly refers to the United States’ overall limited nationwide antimissile program, which has been in development since the 1990s. In contrast to Ronald Reagan’s failed Strategic Defense Initiative system, which was designed to intercept a full-fledged nuclear attack by the Soviet Union in the late 1970s and early 1980s, the current Nation Missile Defense system is only designed to intercept a small number of ICBMs sent by a smaller adversary.
The use of fast interceptor missiles to strike down incoming ICBMs before they detonate is the mechanism of national missile defense, and it is the one currently in place for the United States. Such a missile system would most likely be too slow to respond to submarine-launched ballistic missiles, which could reach their targets in less than a minute after a full-scale nuclear war erupted, but it might be fast enough to respond to ICBMs, which would take 15-20 minutes to reach their targets. Project Nike (late 1950s), Project Defender (early 1960s, never deployed), the Sentinel Program (early 1960s, never deployed), the Safeguard Program (late 1960s, never deployed), and the Strategic Defense Initiative (late 1960s, never deployed) are just a few of the (mostly failed) systems under development (1980s, never deployed).
Rather than pursuing the lofty goal of providing a missile shield capable of repelling an all-out attack, the current National Missile Defense program focuses on protecting the US from nuclear blackmail or a limited attack by a rogue state such as a future North Korea or Iran. As of 2009, ten missile interceptors, as well as a sophisticated radar facility, are stationed in Alaska, a location chosen due to the possibility of North Korean attacks. The system will be deployed in three phases, with the first phase not yet completed as of 2009. The first phase would consist of defending the US against a few dozen missiles without any significant countermeasures. In the late 2010s, functionality would be improved. In contrast to earlier tests that were accused of rigging, the system’s tests in 2002 were successful and viewed as legitimate by the majority of independent commentators.