U.S. uses 'jammers' to guard Iraq convoys

By John J. Lumpkin
The Associated Press

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Roadside bombs have been primary killers of U.S. troops in Iraq. Many go off under passing convoys, killing or injuring the occupants of one of the vehicles.

Gen. Peter Schoomaker, the Army's chief of staff, acknowledged their use in testimony this week before the House Armed Services Committee, but he declined to discuss the bomb defenses in detail. The military does not want to provide useful information to Iraqi insurgents, officials say.

Rep. Gene Taylor, D-Miss., suggested few are being used.

"The Iraqis have figured out if they hit that detonator enough times, they're going to kill a vehicle that does not have a jammer," Taylor told Schoomaker. "The percentage of vehicles that have some form of electronic jammer — it is minuscule, and I know it, you know it, and the Iraq insurgents know it."

But Schoomaker said protection doesn't depend on universal use.

"Every vehicle doesn't have to be equipped," he replied. "You have to have groups of vehicles that have that kind of capability, under an umbrella."

The anti-bomb technology isn't perfect, however. In some cases it only delays a bomb from detonating, so it can still explode and kill bystanders.

The jammers work by preventing a remotely transmitted signal — say, rigged from a cellphone — from detonating an explosive when the bomber presses the button. Depending on the distance, power and design of the jammer, some might prevent the bomb from going off. Others might instead set it off before or after the convoy passes.

Anti-bomb jammers have been in use on vehicles since the early 1980s, said James Atkinson, head of the Granite Island Group, a Gloucester, Mass.-based security and counterespionage firm.

"When you see a car bomb that goes off several blocks away from its intended target, it's usually a dead giveaway it was jammed," Atkinson said.

Military aircraft have used them for decades, and versions of anti-jamming technology are advertised on the Internet. It's unclear if those versions are effective, however.

Depending on their sophistication, jammers can cost from hundreds to millions of dollars. Most can be powered by a car engine.

Some work by transmitting on frequencies that bombers are known to use. Others, called barrage jammers, put out signals on a wide range of frequencies, he said. These will knock cellular phones and CB radios off the air in a given area.

Both kinds can cause a premature or late detonation of a bomb, or prevent it from going off entirely.

It is unclear what defenses exist against other kinds of bombs, such as those that rely on timers or are hard-wired to a switch. Pakistani officials have claimed their jamming devices also interrupted a timer.

Jamming devices carried in the motorcade of Pakistan's President Pervez Musharraf delayed the detonation of a huge bomb that exploded moments after his limousine passed over a bridge near the capital Dec. 14, Pakistani intelligence has said.

Copyright © 2004 The Seattle Times Company