The automotive industry is undergoing the biggest transformation in its 130-year history. Automakers and suppliers around the world are scrambling to develop autonomous vehicles. And, they’re under increasing pressure from outsiders ranging from Silicon Valley tech giants to startup entrepreneurs.

Whenever anyone mentions hybrid-electric vehicles today, most people automatically think of cars, buses and trucks. But, up in the sky, the technology is also getting a lot of attention from aerospace engineers. That’s because electric systems are greener, lighter, quieter and more energy-efficient than traditional alternatives.

Many experts tout fuel cells as one of the cleanest forms of green energy, because the devices reduce CO2 emissions and provide greater energy efficiency than combustion engines.

Within the next decade, a large portion of the U.S. Army’s huge fleet of vehicles could run on battery power. In fact, the Pentagon plans to acquire more than 92,000 electric vehicles by 2020.