anti-ballistic missiles were approximately 90 miles north/northwest of Grand Forks AFB, near Concrete, North Dakota. The missiles were deactivated in 1975. The main radar site (PARCS) is still used as an early warning ICBM radar, facing relative north. It is located at Cavalier Air Force Station, North Dakota. Brief use of Safeguard in 1975/1976 The U.S. Safeguard system, which utilized the nuclear-tipped LIM-49A Spartan and Sprint missiles, in the short operational period of 1975/1976, was the second counter-ICBMs system in the world. Safeguard protected only the main fields of US ICBMs from attack, theoretically ensuring that an attack could be responded to with a US launch, enforcing the mutually assured destruction principle. SDI experiments in the 1980s The Reagan-era Strategic Defense Initiative (often referred to as "Star Wars"), along with research into various energy-beam weaponry, brought new interest in the area of ABM technologies. SDI was an extremely ambitious program to provide a total shield against a massive Soviet ICBM attack. The initial concept envisioned large sophisticated orbiting laser battle stations, space-based relay mirrors, and nuclear-pumped X-ray laser satellites. Later research indicated that some planned technologies such as X-ray lasers were not feasible with then-current technology. As research continued, SDI evolved through various concepts as designers struggled with the difficulty of such a large complex defense system. SDI remained a research program and was never deployed. Several post-SDI technologies are used by the present Missile Defense Agency (MDA). Lasers originally developed for the SDI plan are in use for astronomical observations. Used to ionize gas in the upper atmosphere, they provide telescope operators with a target to calibrate their instruments. Tactical ABMs deployed in 1990s The Israeli Arrow missile system was tested initially during 1990, before the first Gulf War. The Arrow was supported by the United States throughout the 1990s. The Patriot was the first deployed tactical ABM system, although it was not designed from the outset for that task and consequently had limitations. It was used during the 1991 Gulf War to attempt to intercept Iraqi Scud missiles. Post-war analyses show that the Patriot was much less effective than initially thought because of its radar and control system's inability to discriminate warheads from other objects when the Scud missiles broke up during reentry. Testing ABM technology continued during the 1990s with mixed success. After the Gulf War, improvements were made to several U.S. air defense systems. A new