A Glitch in the Patriot Missile System
The tragic consequences of a simple oversight that resulted in the deaths of 28 American troops during the Gulf War in 1991.
The Illusion of Progress
The Gulf War of 1991 painted a picture of American technological prowess. At its heart stood the Patriot missile system. Deployed in 1984, Patriot was initially used as an anti-aircraft system. However, in 1988, it was upgraded to defend against tactical ballistic missiles. During the Gulf War, Patriot created a seemingly impenetrable shield against Iraqi Scud missiles.
However, the veneer of innovation can lead to simple oversights that become deadly. We featured the PowerPoint blunder that contributed to the Columbia tragedy. During the Gulf War, another oversight would result in tragedy.
Death in Dhahran
On February 25th, 1991, that oversight would bear consequences. Patriot’s design features a narrow, highly agile radar array. This is what enables it to detect small, fast targets. Targets like ballistic or cruise missiles and stealth aircraft.
An Iraqi Scud aimed at an American barracks in Dhahran, Saudi Arabia, slipped through the Patriot's net. The missile tore through a building. It killed 28 soldiers and injured nearly 100 others. The illusion of a perfect defense was shattered.
Answers That Drew Anger
American military officials immediately questioned how the missile slipped through the Patriot system. When the General Accounting Office (GAO) released its report in February of 1992, the answer was both shocking and humbling.
They found the error stemmed from a seemingly insignificant error in the Patriot's software. The system’s internal clock used a 24-bit fixed register to produce time in seconds. Due to a chopping error, a rounding issue in calculating time since startup had a cascading effect. Over long periods of operation, the system's internal clock drifted. This threw off its ability to track incoming missiles. The Dhahran battery had been operational for over 100 hours – resulting in a delay of 0.34 seconds.
A Scud missile travels at a speed of 1,676 meters per second. That is more than half a kilometer in the delay window that had occurred. The incoming missile was outside of Patriot’s range gate. The system never saw it. Thus the missile was able to slip through and deliver its devastation.
The Impacts of the Dhahran Tragedy
The GAO report turned shock to anger. A simple mathematical equation showed the oversight. An advanced system failed due to a simple math error. Questions rained down upon the military and its contractors. How could such a critical system harbor such a fundamental flaw? Why wasn't it caught in testing? The finger of blame ultimately pointed towards a culture of overconfidence and a relentless pursuit of rapid deployment.
In a case of tragic irony, the bad time calculation error had been improved in some parts of the code, but not all. As a result, the half-fix contributed to the problem. It prevented inaccuracies from being canceled out. In short, the pressure to get the upgraded Patriot on the battlefield outweighed the need for thorough testing, leaving a digital Achilles' heel exposed.
The Dharan tragedy opened eyes to the vulnerability of complex technological systems. It also made other industries take a second look at their software programs. After all, complex technological systems support air traffic control and financial markets. In a world that now more than ever is dependent on infinite lines of code, Dharan reminds us that a single line of code may possess the power to alter history.
History for the Hurried:
July 20, 1954: An agreement was signed in Geneva, Switzerland, ending hostilities between French forces in Vietnam and the People's Army of Vietnam. The tipping points was a hard learned lesson in Dien Bien Phu.
July 23, 1952: Egyptian army officers launched a revolution changing Egypt from a monarchy to a republic. Van Zandt County tried something similar having grown tired of the United States and Texas.