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High-Tech War
Special Report

The Technology That Changed War

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Only a small percentage of bombs used in 1991 were guided, the rest were old fashioned free-fall "dumb bombs," nearly identical to the kind of bomb that the world's air forces had been dropping with varying degrees of accuracy and large quantities of "collateral damage," ever since the First World War. Nevertheless, the laser bomb's successes prompted an accelerated drive for a better precision weapon. Attention turned to the fast-expanding GPS system.

GPS works like this: Twenty-eight satellites generate radio signals that can be picked up by receivers on the ground or in the air. The receivers can usually "see" between three and four signals at any one time. Once they have a signal, they can calculate the time it has taken for the signal to travel from the satellite. From here on the math is easy. The time taken to travel is multiplied by the speed of light, giving an exact distance between the receiver and a known point in space. Doing this calculation simultaneously from, say, three or four known points in space (i.e. three or more satellites) allows the receiver to triangulate its precise latitude, longitude, and altitude.

DARPA had funded GPS work, initially as an aid to military navigation. Commercial companies had quickly seen the opportunity to offer products to help fishing vessels know their position, or to tell trucking fleets where all their vehicles were. But there had been no direct connection to bombing until engineers at Boeing made a conceptual leap. If a small GPS receiver could be fitted to an old-fashioned bomb, they reasoned, then that bomb, just like a truck or a trawler, could "know" its position, in three dimensions and in real time. Could it then guide itself, they asked, to a target whose position the bomb also "knew"?

The answer was "Yes," because powerful computers could calculate the difference between where it was and where its target was. Having done that, the computer could control moveable fins on the rear of the bomb, so as to make the bomb's current position eventually match the target position, literally "flying" the bomb towards its target.

The growing availability in the mid to late 1990s of small, cheap computers with vastly increased data-processing power was critical here, allowing the many millions of calculations necessary to update the bomb on its position every second, calculate the adjustments necessary and pass them to the fins.

The combined power and precision of GPS and the JDAM allowed the U.S. government to use military power in an entirely new way. It is very unlikely that President Clinton would have authorized war over Kosovo in 1999 had it looked like an old-fashioned ground and air campaign, with all the risks of U.S. casualties that that would have involved. But, instead, the newly introduced 1,000- and 2,000-pound JDAM allowed General Wesley Clark's NATO forces to strike from high in the sky, mostly beyond the reach of Serbian air defenses, and to slowly degrade enemy facilities and morale.

Although there were some notable mistakes (such as bombing the Chinese embassy), these tended to be the result not of faulty technology, but human error: entering mistaken coordinates into the bomb. The JDAM itself went exactly where it was told to go.

GPS-JDAM demonstrates how technology offers new foreign policy options. For example, the GPS-JDAM connection is largely responsible for the ultimate capitulation of the Serbian military, which played a role in the fall -- and later arrest -- of the Serbian dictator Slobodan Milosovic. During the air campaign, no pilots' lives were lost while flying combat missions.

After 9-11, the JDAM gave the Pentagon the opportunity to hit America's new enemies quickly and at extreme long range. Afghanistan, unreachable by large numbers of U.S. ground troops, was nevertheless in range of long-range bombers and carrier-based aircraft, all armed with JDAMs, and of U.S. Navy cruise missiles guided to their targets by GPS. Once the Afghan ground war began in earnest, a few hundred U.S. "spotters" on the ground were able to provide coordinates to attacking warplanes and quickly wreak havoc with the enemy's military and political infrastructure. Pundits predicted a quagmire in Afghanistan similar to that faced by the old Soviet Army in the same region. But the Soviets had not had JDAMs.

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Jet dropping bomb
An F-16 Fighting Falcon launches a JDAM guided bomb.
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A night vision image of downtown Baghdad, under attack in 2003.
A night vision image of downtown Baghdad, under attack in 2003.
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