Strategic Defense Initiative

Missile Defense Test

A U.S. interceptor missile lifts off from Kwajalein Atoll in the Pacific Ocean in December 2001 in a test of a missile defense system. The interceptor successfully destroyed a Minuteman II missile in space, but officials with the U.S. Ballistic Missile Defense Organization said the test was not carried out under realistic conditions. Defense against intercontinental ballistic missiles has long been controversial because of its costs, doubts about its reliability, and its effect on arms control agreements.

Strategic Defense Initiative (SDI), United States military research program for developing an antiballistic missile (ABM) defense system, first proposed by President Ronald Reagan in March 1983. The Reagan administration vigorously sought acceptance of SDI by the United States and its North Atlantic Treaty Organization (NATO) allies. As initially described, the system would provide total U.S. protection against nuclear attack. The concept of SDI marked a sharp break with the nuclear strategy that had been followed since the development of the armaments race. This strategy was based on the concept of deterrence through the threat of retaliation (see Arms Control). More specifically, the SDI system would have contravened the ABM Treaty of 1972 (see Strategic Arms Limitation Talks). For this reason and others, the SDI proposal was attacked as a further escalation of the armaments race.

Many experts believed the system was impractical. With the dissolution of the Soviet Union, the signing of the START I and II treaties, and the election in 1992 of Bill Clinton as president, the SDI, like many other weapons programs, was given a lower budgetary priority. In 1993 U.S. secretary of defense Les Aspin announced the abandonment of SDI and the establishment of the Ballistic Missile Defense Organization (BMDO) to oversee a less costly program known as National Missile Defense that would make use of ground-based antimissile systems.

The SDI system was originally planned to provide a layered defense employing advanced weapons technologies, several of which were only in a preliminary research stage. The goal was to intercept incoming missiles in midcourse, high above the earth. The weapons required included space- and ground-based nuclear X-ray lasers, subatomic particle beams, and computer-guided projectiles fired by electromagnetic rail guns—all under the central control of a supercomputer system. (The space-based weapons and laser aspects of the system gained it the media name “Star Wars,” after the popular 1977 science-fiction film.) Supporting these weapons would have been a network of space-based sensors and specialized mirrors for directing the laser beams toward targets. Some of these weapons were in development, but others—particularly the laser systems and the supercomputer control—were not certain to be attainable.

The total cost of such a system was estimated at between $100 billion and $1 trillion. Actual expenditures for SDI amounted to about $30 billion. The initial annual budget for BMDO was $3.8 billion.

Cost was not the only controversial issue surrounding SDI. Critics of SDI, including several former government officials, leading scientists, and some NATO members, maintained that the system—even if it had proved workable—could have been outwitted by an enemy in many ways. Also, other nations feared that the SDI system could have been used offensively.

The administration of President George W. Bush gave missile defense a high priority when Bush took office in January 2001. The September 11 terrorist attacks that year gave further impetus to a missile defense system. Secretary of Defense Donald Rumsfeld said such a system was needed to protect the United States from possible attacks by terrorist groups or rogue states. In 2002 the Bush administration withdrew from the ABM Treaty so that it could pursue more vigorous testing of a missile defense program. Criticism of a missile defense system persisted. The Union of Concerned Scientists said the technology did not yet exist to deploy a reliable missile defense system. The group also argued that countermeasures could easily be taken against such a defense system. Other critics noted that terrorists would be unlikely to use missiles and could conceal nuclear weapons, if they obtained them, in a ship or van.