<P> The Strategic Defense Initiative ( SDI ) was a proposed missile defense system intended to protect the United States from attack by ballistic strategic nuclear weapons ( intercontinental ballistic missiles and submarine - launched ballistic missiles ) . The concept was first announced publicly by President Ronald Reagan on 23 March 1983 . Reagan was a vocal critic of the doctrine of mutual assured destruction ( MAD ) , which he described as a `` suicide pact '' , and he called upon the scientists and engineers of the United States to develop a system that would render nuclear weapons obsolete . </P>
what was the main goal of the strategic defense initiative
to protect the United States from attack by ballistic strategic nuclear weapons ( intercontinental ballistic missiles and submarine - launched ballistic missiles )