(CNN) -- A silent, invisible battle is being fought against roadside bombs in Iraq. Though the military doesn't like to advertise their use, electronic jamming systems are playing a key role in neutralizing the threat.



Smoke billows from tires of a U.S. military truck hit by an IED near the Iraqi-Syrian border in October 2005.



"Any weapon we had against IEDs, [improvised explosive devices] was utilized including jamming technology," said Jason Spencer, 29, an Oklahoma City, Oklahoma, engineer who served with the Army in Iraq in 2005.



Vehicle mounted electronic jammers attempt to block a signal going to a radio-controlled IED. The military also uses portable backpack jammers.



"The sophistication of IEDs definitely increased during my time in Iraq," said Spencer. "There was a definite increase in remote detonation."



A signal going to a remote-controlled IED operates on a radio or infrared frequency.



Jamming devices, known as Counter Radio Controlled Improvised Explosive Device Electronic Warfare, or CREW systems, attempt to intercept or block a signal before it reaches its intended target, preventing detonation.



One common method is barrage jamming, which knocks out a broad range of radio signals. However, it also knocks out communications used by U.S. troops putting them at increased risk.



"Ideally what you want to be able to do is have something that can grab very precise signals, capture the signals and render them irrelevant without knocking out your own communication," said CNN military analyst retired Army Brig. Gen. James "Spider" Marks.



These technologies represent the last line of defense, Marks said. "We don't want to give our potential enemies an understanding of what we are doing to counter their efforts," he said.



Along with jammers, troops use air surveillance, robots, blast-resistant vehicles and mine rollers as countermeasures.  See counter-IED technologies in Iraq »



IEDs are the No. 1 source of U.S. and alllied casualties in Iraq, according to the Department of Defense. From July 2003 to July 2007, 1,565 coalition forces were killed by IEDs, according to iCasualties.org.  See the casualty toll inflicted by IEDs »



"We dealt with hundreds of IEDs while in theater," said Spencer. "IEDs were always on our minds during every patrol."



Spencer says IEDs come in a variety of shapes and sizes. "From a simple mortar round on the side of the road with a fuse and a wire running to a push-button, to complex explosives poured into concrete (shaped like curbs) with remote detonators and booby traps."



Most roadside bombs are remotely detonated using common household devices: cell phones, garage door openers, burglar alarms, key fobs, doorbells, or remote controls for toy cars.  Learn more about the IED threat »



"Our enemy hides in plain sight. He buys his bomb parts in stores. It's standard commerce," said Marks.



U.S. forces are dealing with an adaptive, innovative and flexible enemy, according to the Joint Improvised Explosive Device Defeat Organization, or JIEDDO, which is leading the counter-IED effort for the military.



As insurgents modify their devices to outwit the military, the military in turn adapts its own jamming technologies.



Many companies have been tapped to supply jammers to coalition forces. JIEDDO is interested in technologies that can be used in the field within two to eight months -- "light speed" in Defense Department terms.



The Army's main CREW system is the Warlock Duke, a vehicle- mounted radio jammer developed by Syracuse Research Corporation. It's capable of jamming most radio-controlled IEDs, according to the Pentagon.



The Navy, which oversees the CREW program, contracted BAE Systems to produce 3,800 wearable jammers to be fielded in Afghanistan and Iraq in 2008.



Canadian firm Med-Eng is building jammers for the Marines, reports military contractor General Dynamics.



By the end of 2007, JIEDDO will have funded more than 30,000 jammers for Marine and Army units. They have spent $1.6 billion on jamming technology for this fiscal year.
What was used to block an IED from detonating? what did they block
Vehicle mounted electronic jammers signal
question: What was used to block an IED from detonating?, answer: Vehicle mounted electronic jammers | question: what did they block, answer: signal