Pursuant to a congressional request, GAO reviewed the facts associated with the failure of a Patriot missile defense system in Dhahran, Saudi Arabia, during Operation Desert Storm. 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.