The Pentagon has been researching nonlethal pain rays since the mid-’90s, but finding a vehicle to carry them has proven to be a challenge. Researchers have mounted these microwave weapons—which repel people by heating water molecules just under the skin, reportedly without damaging tissue—on trucks, guard towers and Humvees, but the U.S. military has never deployed them for real-world use. (Using such weapons on civilians in Iraq or Afghanistan is not seen as a good way to win hearts and minds.)

Undaunted, the Air Force is now trying to install pain rays on Special Operations gunships, which are 98-foot-long AC-130 aircraft originally designed to haul cargo. The Airborne Active Denial System would require a beam generator of unprecedented size, says Diana Loree, manager of the program at the Air Force Research Lab. Megawatt microwave generators (called gyrotrons) already exist, producing intense heat in plasma-research laboratories and factories that need to melt glass or composite materials, but the military program requires a generator twice as large as any existing model. AFRL staff hope to demonstrate a giant gyrotron during ground tests in 2014, Loree says. Special Ops forces might welcome an overhead nonlethal weapon that disperses mobs or stops people from advancing on downed aircraft. Also, the use of an energy weapon during a clandestine mission would be less prone to public outcry.

Active Denial System (ADS) microwave weapons work well in tests but don’t get used much. The U.S. Army’s Project Sheriff mounted ADS on a light armored vehicle, along with dazzling lights and sonic blasters; the hardware was ready in 2005 but was never fielded. In October, Raytheon said it sold a lower-power version of ADS called Silent Guardian to a foreign buyer and to a U.S. law-enforcement agency, but will not identify the customers.

Courtesy of David Hambling, Popular Mechanics