Most drones today use internal combustion engines that are extremely loud, which forces officials to fly them at higher altitudes during missions.

"Think about lawnmowers or chainsaws -- they're really loud," Naval Research Lab researcher Karen Swider-Lyons told LiveScience during a recent interview.  "It's hard to spy on people when they know you're there, so you had to fly them at high altitudes to keep them from being heard."

The Office of Naval Research said spy planes powered by electric engines are available, but they have shorter estimated flight times than aircraft powered by internal combustion engines.

To help fill a void in next-gen technology, the "Ion Tiger" UAV is powered by hydrogen fuel cells.  The engines can run quieter than a regular engine, while also being twice as efficient, offering an appealing alternative as the USAF increases the use of spy planes.  

During testing in October, Ion Tiger flew 23 hours and 17 minutes consecutively, though that number was recently topped while flying over the "Aberdeen Proving Ground."  The 37-pound craft flew for 26 hours and 1 minute.

The military has announced different ways it looks to go green, ranging from hybrid Humvees to greener Navy ships -- but this is the first significant proof showing a UAV successfully powered by alternative energy.

The newer drones could also fly civilian routes to observe natural disasters, track storms, or provide surveillance, military experts said.