A group at Georgia Tech has devised a unmanned aerial vehicle that flies on a hydrogen fuel cell.
The craft, which has a wingspan of 22 feet, has made several flights lasting up to a minute. Fuel cell UAVs could offer some distinct advantages. One, they are quiet, which, considering that UAVs are used for battlefield reconnaissance, is important. Two, they leave a more faint heat signature than UAVs on electric motors, so they potentially won't get picked up by counterintelligence systems as easily.
Soldiers wouldn't need generators to charge the engine. Then again, they'd need to lug around cylinders of compressed hydrogen.
The project fits firmly into two major thrusts by the Department of Defense: increase the use of robots in battle and switch to alternative fuel.