During the final days of hostilities in the first Gulf War, on February 25, 1991, an Iraqi Scud missile killed 28 American service men and women.
The war ended on February 28, 1991.
The Patriot missile system, until then, had a good track record of intercepting slow moving, incoming Scud missiles. Tragically, an inaccurate time calculation caused the system to fail to recognize the incoming Scud missile as a threat. As a result, the Patriot battery did not fire at the incoming missile. Had it fired, it may have intercepted the Scud.
The failure was because the Patriot system was kept up and running for too long, over 100 hours, resulting in a timing error.
Here is the official report made to Congress by the General Accounting Office about this incident:
Information Management and Technology Division
B-247094
February 4,1992
The Honorable Howard Wolpe Chairman, Subcommittee on Investigations and Oversight Committee on Science, Space, and Technology House of Representatives
Dear Mr. Chairman:
On February 25, 1991, a Patriot missile defense system operating at Dhahran, Saudi Arabia, during Operation Desert Storm failed to track and intercept an incoming Scud. This Scud subsequently hit an Army barracks, killing 28 Americans. This report responds to your request that we review the facts associated with this incident and determine if a computer software problem was involved. If so, you asked that we provide information on what the specific software problem was, and what has been done to correct it. Appendix I details our objectives, scope, and methodology.
Results in Brief
The Patriot battery at Dahahran failed to track and intercept the Scud missile because of a software problem in the system’s weapons control computer. This 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 over 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 been used to defend against Scud missiles 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 8 consecutive hours. Consequently, Army officials modified the software to improve the system’s accuracy. However, the modified software did not reach Dhahran until February 26,1991-the day after the Scud incident.
For more detail, see:
https://www.gao.gov/assets/220/215614.pdf