The measures and weapons systems designed to protect the United States against an enemy intercontinental ballistic missile strike. Among the elements of the U.S. national missile defense system deployed or contemplated since the early 1960s were the Nike Zeus missile, the Sentinel and Safeguard systems, the Strategic Defense Initiative (SDI; the so-called “Star Wars” program), and the Global Protection Against Limited Strikes (GPALS) system.
See the Introduction, Abbreviations and Pronunciation for further details.