Next month, in naval exercises off the coast of Hawaii, five U.S. warships will make history: They will be the first to use biofuels to power their huge turbines, as well as the jet planes screaming off a carrier’s deck and helicopters hovering overhead.

The flotilla—powered by a mixture of cooking grease and algae oil—is the centerpiece of the U.S. Navy’s efforts to shake off its centurylong dependence on petroleum.

The exercises have become the center of a political maelstrom. Last month, both houses of Congress voted to stop the NAVY from buying alternative fuel priced higher than oil. 

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