By Sharon Weinberger of Nature magazine
For some Pentagon officials, the demonstration in October 2007 must have seemed like a dream come true — an opportunity to blast reporters with a beam of energy that causes searing pain.
The event in Quantico, Virginia, was to be a rare public showing for the US Air Force's Active Denial System: a prototype non-lethal crowd-control weapon that emits a beam of microwaves at 95 gigahertz. Radiation at that frequency penetrates less than half a millimeter into the skin, so the beam was supposed to deliver an intense burning sensation to anyone in its path, forcing them to move away, but without, in theory, causing permanent damage.
However, the day of the test was cold and rainy. The water droplets in the air did what moisture always does: they absorbed the microwaves. And when some of the reporters volunteered to expose themselves to the attenuated beam, they found that on such a raw day, the warmth was very pleasant.
A demonstration of the system on a sunny day this March proved more successful. But that hasn't changed a fundamental reality for the Pentagon's only acknowledged, fully developed high-power microwave (HPM) weapon: no one seems to want it. Although the Active Denial System works (mostly) as advertised, its massive size, energy consumption and technical complexity make it effectively unusable on the battlefield.
The story is much the same in other areas of HPM weapons development, which began as an East–West technology race nearly 50 years ago. In the United States, where spending on electromagnetic weapons is down from cold-war levels, but remains at some US$47 million per year, progress is elusive. “There's lots of smoke and mirrors,” says Peter Zimmerman, an emeritus nuclear physicist at King's College London and former chief scientist of the US Arms Control and Disarmament Agency in Washington DC. Although future research may yield scientific progress, he adds, “I cannot see they will build a useful, deployable weapon”.
For many critics, the US HPM program has become a study in wishful thinking, exacerbated by a culture of secrecy that makes real progress even more difficult.
The quest to build an electromagnetic weapon — an e-bomb, in military jargon — was sparked on 8 July 1962, when the United States carried out Starfish Prime, the largest high-altitude nuclear test that had ever been attempted. The 1.4-megaton thermonuclear warhead, detonated 400 kilometers above the central Pacific Ocean at 9 seconds past 11 p.m., Hawaii time, blasted huge swarms of charged particles outwards along Earth's magnetic field. Their gyrations generated a pulse of microwave energy that drove measuring instruments off the scale. Artificial auroras lit up the night across swathes of ocean. And in Honolulu, more than 1,300 kilometers from the detonation point, the pulse set off burglar alarms, knocked out street lights and tripped power-line circuit breakers.
Nothing like Starfish Prime has been seen since August 1963, when the Partial Test Ban Treaty outlawed nuclear explosions anywhere but underground. But the test showcased the potential destructiveness of an electromagnetic pulse to military planners on both sides of the cold-war divide, and launched them into a race to harness it as a weapon using a non-nuclear source.
The US Air Force has been the main funder of the country's HPM program from the beginning. At first, its goal was a weapon capable of taking out an enemy's computers, communication systems and other electronics. In theory, the idea remains compelling: an e-bomb would be able to fire microwave 'bullets' at the speed of light and, if tuned to the right frequencies, disable its targets without collateral damage. Cars could be stopped in their tracks, radars blinded and computers destroyed, with no need for high explosives.