'Jammers' help protect convoys 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, so 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.

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.

"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.

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.

Since then, Pakistan has imported more jamming devices for security of VIPs, a senior government official told The Associated Press on the condition of anonymity Thursday. He refused to give further details, including where the devices were imported from, citing security reasons.

In Israel, a special unit in the Ministry of Defense developed jamming technology in the early 1990s and used it extensively in southern Lebanon in the mid- to late 1990s in an effort to neutralize roadside charges placed by Hezbollah.

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 claimed their jamming devices also interrupted a timer.

In Iraq, employing the jammers is one of a number of steps the military is taking to protect vehicles and soldiers. Others include deploying a more heavily armored Humvee and giving soldiers improved body armor.

"We've taken some major moves there that are paying off, in my view." Schoomaker said.

In Baghdad, a military official said the Iraqi bombs have varied widely in sophistication.

"Our soldiers have become ... very adept at noticing, observing," said Brig. Gen. Vincent Boles, commander of the 3rd Corps Support Command. "We're discovering more than are exploding."