Burning petroleum is a big problem for the Pentagon. It’s expensive: Destroyers use a thousand gallons an hour. And because ships burn through so much, they must make frequent pit stops for fuel, either at port or in a rendezvous with a tanker. That’s why the U.S. Naval Research Laboratory (NRL) has spent years researching the possibility of extracting liquid hydrocarbon from seawater to power its ships.

In addition to H20 and salt, ocean water is rich in carbon dioxide. (Make that very rich: Navy scientists say the CO2 concentration is 140 times that of air.) So the Navy built a large system including a catalytic converter that extracts hydrogen and carbon dioxide from the water with 92 percent efficiency and then — via a reaction with a metal catalyst — transforms those gases into a liquid hydrocarbon fuel that the ship’s existing engines can burn. In a proof-of-concept test held last week, naval researchers made enough of the stuff to fly the model plane with its small off-the-shelf engine.

With the test flight a success, the Navy now must prove it can produce sea-based fuels in mass quantity. Researchers will start by setting up test production facilities on land. Eventually, the goal is to turn the catalytic converter into something no larger than a car that can live aboard a ship and supply its fuel by processing seawater.

Within a decade, the Navy says, it will be able to make hydrocarbon fuel from the ocean at a cost of $3 to $6 per gallon, and that’s about the range they need to be in. The Navy currently spends $3.50 to $4 per gallon.

“NRL has developed a game-changing technology for extracting, simultaneously, CO2 and H2 from seawater,” NRL’s Heather Willauer says. “This is the first time technology of this nature has been demonstrated with the potential for transition, from the laboratory, to full-scale commercial implementation.”