Strategic Defense Initiative

Strategic Defense Initiative (SDI), United States military research program for developing an antiballistic missile (ABM) defense system, first proposed by President Ronald Reagan in 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 protection of the United States against a 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. 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 arms race.

Many experts believed the system was impractical. With the dissolution of the Union of Soviet Socialist Republics in 1991, 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 nickname “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 the program, including several former government officials, leading scientists, and some NATO members, maintained that the system—even if it had proved workable—could have been defeated by an enemy in a variety of ways. Also, other nations feared that the SDI system could have been used offensively by the United States.

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 (see Terrorism). In 2002 the Bush administration withdrew from the ABM Treaty so that it could pursue more-vigorous testing of a missile defense program. The same year the BMDO was renamed the Missile Defense Agency, but the efforts continued to draw criticism from scientists and other nations. See also Air Defense Systems; Warfare; Arms Control; Guided Missiles; Nuclear Weapons.