The U.S. military burns about 12 million gallons of oil every day, but the Navy is trying to reduce that number.
It's experimenting with alternative fuels, with the goal of a permanent Green Fleet deployment by 2016.
Not everyone is on board with this. Senator John McCain says it's too expensive and that adopting a "green agenda for national defense, of course, is a terrible misplacement of priorities."
But the Navy is steaming ahead.
Julia Whitty, environmental correspondent for Mother Jones magazine, saw the Green Fleet in action last summer. She wrote about it in a piece called "My Heart-Stopping Ride Aboard the Navy's Great Green Fleet."
In this video, she talks about the experience of landing on an aircraft carrier in a plane fueled with a 50-50 blend of biofuel and aviation fuel:
This segment aired on March 4, 2013.