When Erwin Rommel's Panzer tanks ran out of diesel fuel in North Africa in World War II, the German general poured cooking oil into their gas tanks to keep the vehicles fighting.

The U.S. military thinks Germany's "Desert Fox" might have been onto something. At bases throughout the United States, soldiers are filling their gas tanks with biodiesel – diesel fuel made from soybean or other vegetable oil.

The Marines are among those leading the charge. At Camp Pendleton, just north of San Diego, for example, the semis that haul the Marines' 70-ton M-1 tanks have been running B20, a mix of 20 percent biodiesel and 80 percent petroleum diesel, for more than two years. So have the buses and trucks that carry the troops and their gear, forklifts, generators – even a diesel locomotive in the base's switchyard.

So far, the military is not running biodiesel in tanks or other equipment that could get sent into battle zones. But at bases in the United States, use of the environmentally friendly fuel is growing rapidly. In 2003, the Marine Corps used 844,000 gallons of B20 biodiesel, says retired Navy Cmdr. Leo Grassilli, a military biodiesel expert. This year, Camp Pendleton and other nearby bases alone expect to use more than a million gallons. "We've been told we're the No. 1 user of biodiesel in the U.S.," says Gary Funk, the fleet manager for Marine Corps vehicles there.

The other military services are also turning to biodiesel. The naval station at Everett, Washington, has been running the fuel since 2001. So has Peterson Air Force Base near Colorado Springs, Colorado. Biodiesel can be found on at least 40 more Air Force bases, according to the National Biodiesel Board.

All told, the military will use more than 6 million gallons of biodiesel this year, according to the Defense Energy Support Center, the government agency that supplies the military with fuel. That's still a drop in the bucket compared to the military's overall fuel needs, however. The Navy and Marine Corps burn through nearly 2 billion gallons of diesel a year, says Grassilli.

Biodiesel use in the military is just beginning to take off. Earlier this year, the Department of the Navy ordered all Navy and Marine installations in the United States to begin using biodiesel when possible. Large naval bases such as the one at Norfolk, Virginia, are installing additional fuel tanks specifically for biodiesel. The Navy is even experimenting with brewing its own biodiesel from the used vegetable oil that comes out of its mess halls.

One advantage of biodiesel, say military officials, is that it delivers the same performance as petroleum diesel, but is far less damaging to the environment. "There's no loss of power, and we get the same mileage," says Donald Schregardus, deputy assistant secretary of the Navy for environmental programs, "and the vehicles are cleaner. You don't get the soot that you get out of regular diesel."

Environmental Protection Agency studies on the fuel show that it produces less carbon monoxide, particulate matter and smog-producing hydrocarbons than standard diesel.

That's important to the military's role as a public citizen, says Funk. "We operate our vehicles on the public highways," he says. "Biodiesel sends a signal to the American public that we're working to keep the air clean, and to reduce our dependence on foreign oil."

The new fuel is also helping the military meet a presidential mandate to federal agencies, the Energy Policy Act of 1992, that requires the government agencies to begin using alternative fuel vehicles. It's also helping them meet a congressional mandate to the military to reduce their fuel use by 20 percent. So far, the Marine Corps is the only service to have met that goal, in large part thanks to biodiesel.

Initially, biodiesel faced some skepticism from fleet managers and military procurement officials who were used to fuel that was pumped out of the ground, rather than grown on top of it. But now, top brass are solidly behind it. "The Navy has been very pleased with biodiesel," says Schregardus.

Biodiesel's track record at places like Camp Pendleton has helped. "We're hauling tanks up grades that average 7 percent for a couple of miles, and we've had absolutely no problems with it," Funk says.

Biodiesel's increasing popularity in the civilian world hasn't hurt, either. Other federal agencies, including the U.S. Postal Service, the Department of Agriculture and NASA are using it. So are many local governments. Snowplows in Minneapolis, school buses in Virginia and New Jersey, and aircraft rescue trucks at the Lambert-St. Louis International Airport all run on biodiesel. And starting this week, a state law in Minnesota will require all diesel fuel sold there to contain at least 2 percent biodiesel.

It hasn't hurt that it's far easier to switch to biodiesel than to other alternative technologies like electric or compressed natural gas vehicles. At Camp Pendleton, Funk says, "we just began pouring it into the fuel tanks." Not only were no modifications to the engines required, but the base's drivers didn't even notice the change. "Until we stenciled 'Powered by Biodiesel' on the sides of the cabs more than a year later," he says, "none of them knew."

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