Final answer:
The Strategic Defense Initiative (SDI) was envisaged to protect the United States from nuclear intercontinental ballistic missiles (ICBMs), using a system that might include armed satellites which could shoot down incoming missiles.
Step-by-step explanation:
The Strategic Defense Initiative (SDI) was designed to protect the United States from intercontinental ballistic missiles (ICBMs) carrying nuclear warheads. Often referred to by the nickname "Star Wars," SDI was a concept for a defensive system that could theoretically employ various technologies, including armed satellites and modern countermeasures, to shoot down these missiles before they could reach their targets.
SDI aimed to provide a technological edge over the threat of a nuclear attack and was a departure from the traditional concept of deterrence that underpinned the Mutual Assured Destruction (MAD) doctrine. This initiative was part of a broader strategy of the United States during the Cold War to reinforce its military capabilities and to provide a potential shield against a Soviet missile strike.