DevotedSkeptic writes in with a story about the lack of usable microwave technology to come from 50 years of military research. "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 millimetre 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. 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.'"