Also known as S.D.I. and Star Wars. S.D.I. was announced by President Ronald Reagan in 1983. It was designed to create a completely new form of national defense, through the creation of a defensive shield around the United States, which would allow incoming nuclear weapons to be destroyed by laser guns before they hit their target.

Reagan believed that S.D.I. could put an end to nuclear weapons by making them useless. However, many experts were certain that S.D.I. could not possibly work at all; others said it could not protect the entire U.S. population and would merely force the Soviet Union to aim more nuclear warheads at the U.S. But in spite of these concerns, the Reagan administration committed large resources to the development of S.D.I., and it was an important factor in negotiations with the Soviet Union during Reagan's two terms of office. (The Soviets opposed the development of S.D.I.) The administration of President George H. W. Bush (1989-1993) was less enthusiastic about Star Wars, and the idea gradually was dropped, especially since the end of the Cold War made a nuclear attack on the U.S. less likely. Research into anti-missile defence systems still continues, however.