Patriot Missile Defense

Because of a software problem in the Patriot missile defense system, the Patriot battery at Dhahran, Saudi Arabia, failed to track and intercept an incoming Iraqi Scud missile that later struck an Army barracks, killing 28 Americans. The computer problem led to an inaccurate tracking calculation that became worse the longer the system operated. At the time of the incident, the battery had been operating continuously for more than 100 hours. By then, the inaccuracy was serious enough to cause the system to look in the wrong place for the incoming Scud. The Patriot had never before defended against a Scud missile nor was it expected to operate continuously for long periods of time. Two weeks before the incident, Army officials received Israeli data indicating some loss in accuracy after the system had been running for eight consecutive hours. Consequently, Army officials modified the software to improve the system's accuracy. The modified software did not reach Dhahran, however, until February 26, 1991--the day after the Scud episode.

GAO found that: (1) the Patriot battery at Dhahran failed to track and intercept a Scud missile due to a software problem in the system's weapons control computer; (2) the software problem caused an inaccurate tracking calculation which became worse the longer the system operated; (3) at the time of the incident, the battery had operated continuously for over 100 hours and the inaccuracy was serious enough to cause the system to look in the wrong place for the incoming Scud; (4) two weeks before the incident, Army officials received Israeli data indicating some loss in accuracy after the system had been running for 8 consecutive hours; (5) the Army had never used the Patriot to defend against tactical ballistic missiles or expected the Patriot to operate continuously for long periods of time; and (6) Army officials modified the software, but the new software did not reach Dhahran until the day after the incident.