WASHINGTON - Test subjects can't see the invisible beam from the Pentagon's new, Star Trek-like weapon, but no one has withstood the pain it produces for more than three seconds.
People who volunteered to stand in front of the directed energy beam say they felt as if they were on fire. When they stepped aside, the pain disappeared instantly.
The long-range column of millimeter-wave energy is known as the "Active Denial System" for its ability to prevent an aggressor from advancing. Senior military officials, who plan to deliver the device for troop evaluation this fall, say years of testing has produced no sign it will lead to health effects beyond perhaps causing skin to temporarily redden.
It is among the most potent of a new generation of futuristic, "less-than-lethal" weapons being developed by the Defense Department - tools that could dramatically alter the way police control riots and soldiers fight wars.
Other nonlethal devices undergoing tests include "superlubricants" that could make a road or runway too slippery for car or airplane tires to gain traction; directed sound waves to drive people away from an area; and nets able to stop cars.
Marine Col. David Karcher, who heads the Pentagon's Joint Non-Lethal Weapons Directorate, says the energy beam is aimed at helping troops and police in confusing situations by offering options "between bullets and a bullhorn."
Marine Capt. Dan McSweeney, a spokesman for the Non-Lethal Weapons Directorate, pointed to "instances in Iraq where crowd situations have unfortunately ended in violence" and death.
Karcher and other military officials are trying to alleviate fears that the device might be misused to harm civilians or converted into a torture machine that leaves no marks.
In an attempt to anticipate how the world would greet the new weapon, the Air Force this month asked social science graduate students at the University of Minnesota and other colleges for help.
Researchers were offered $12,000 to spend the summer reviewing literature and assessing how Americans and other cultures might react to its use.
In the solicitation, Maj. Jonathan Drummond of the Air Force's Directed Energy Bioeffects Division noted that the Active Denial System could provide U.S. forces "with a nonlethal capability in military operations other than war." Among possible uses, he listed peacekeeping, humanitarian operations and crowd control.
Introduction of such a device in either noncombat or wartime situations could raise thorny questions: Would it be acceptable to inflict so much pain on unruly protesters? How would such a weapon be viewed if used on crowds in Third World countries? Would it violate international humanitarian principles if used in battle? Might it be used secretly during interrogations to torture suspected terrorists into cooperating?
Karcher said the Active Denial System "is absolutely not designed or intended or built" to be a torture device.
"To use this as any sort of torture device would be in direct violation of" the Pentagon's definition of nonlethal weapons, he said. "Nor, as professionals, would any of us sign up for it."
But in an era of secret interrogations of al-Qaida suspects and revelations of U.S. abuse of prisoners at Iraq's Abu Ghraib prison, Executive Director Doug Johnson of the Minneapolis-based Center for Torture Victims is skeptical.
"It seems fundamentally a weapon that's designed to create a great deal of pain and fear," Johnson said. "The concern I would have is ... once this kind of technology is available and there's a perception that it's safe and nonlethal, it seems like a natural device to be used in interrogations.
"Is it torture if it only creates a sensation of pain, but leaves no marks and no long-term damage? I would say yes. Torture is primarily a psychological device, and finding different ways to use the body against the mind has been the struggle of torture technologies for thousands of years."
He said "human history would demonstrate" that once a potential torture technology is available, it usually is put into action.
Karcher and other military officials stressed that the device has received interim approvals from international treaty conventions, has twice passed Pentagon legal reviews and will be subject to clear rules of engagement.
Eleven years in the making at a cost of more than $50 million, the Active Denial System is still years from deployment. It weighs about 4 tons and consists largely of a big dish and antenna that are mounted on a Humvee multipurpose vehicle.
But researchers are hoping to miniaturize it, Karcher said. Air Force officials want to work with the prime contractor, the Raytheon Corp., to design a version that could be mounted on a military transport plane so its beam could cut a broader swath on a battlefield.
Once an operator has aimed the antenna using a scope, the press of a button sends out a column of millimeter-wave, electromagnetic energy at the speed of light. Pentagon officials say that the weapon's exact reach and its column size are classified, but that it can extend beyond the 550-meter effective range of bullets. Its intensity is the same at any distance.
Susan Levine, the Pentagon's project manager for the energy beam, said years of tests on humans and animals enabled researchers to establish a margin of safety. After several seconds, the device automatically shuts off to avoid burning its target, she said.
When the beam hits an individual, it penetrates 1/64th of an inch beneath the skin and heats water molecules to 130 degrees in less than a second.
"It tricks the pain sensors into thinking they're on fire," said Rich Garcia, a spokesman for the Air Force Research Laboratory at Kirtland Air Force Base in Albuquerque, N.M.
Garcia knows firsthand. He was among hundreds of test volunteers, standing in a doorway with his back facing the device.
"They did a full body back shot," he said. "It hit in the small of my back first. For the first millisecond, it just felt like the skin was warming up. Then it got warmer and warmer and you felt like it was on fire."
He said he lunged out of the doorway.
"As soon as you're away from that beam your skin returns to normal and there is no pain," Garcia said. "I thought to myself, 'Why you wimp. You know it's not causing any damage. You'll be able to override it.' Each of the next three times, I was on there a little bit longer.
"The fourth one was the longest. It was about two seconds. It felt like my hair was on fire."
The beam easily penetrates clothing, he said, because clothes are porous, though a thin suit of armor would block it.