Jammers protecting troops in Iraq

WASHINGTON — U.S. soldiers riding in convoys in Iraq are relying on electronic "jammers" to help protect against the roadside bombs insurgents have used to deadly effect.

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

It's unclear how widely the jammers — the same technology that saved Pakistan's leader from a recent assassination attempt — are being used in Iraq.

Gen. Peter J. 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 said. "You have to have groups of vehicles that have that kind of capability, under an umbrella."

The jammers work by preventing a remotely transmitted signal — say, rigged from a cell phone — 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 — potentially wreaking havoc on bystanders.

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.

But in some cases, they have gone off only after a convoy has passed.

That can be a sign that a jammer on one of the vehicles did its job, said James Atkinson, head of the Granite Island Group, a Gloucester, Mass.-based security and counterespionage firm.

Anti-bomb jammers have been in use since the early 1980s, 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. Guerrillas frequently rig remote-controlled detonators out of garage door openers, car alarm remotes or cellular phones, Atkinson said.