The Department of Defense, once known as one of the nation’s largest polluters, is turning to sustainability to reduce ballooning energy costs and the logistical risks of transporting fuel in combat zones. “By operating more efficiently and by incorporating energy and sustainability considerations into our plans and operations, we can create a more agile, lethal, tactical, and effective combat force,” Sharon Burke, the Defense Department’s assistant secretary for operational energy, said at an energy forum in April.

The Department of Defense spent nearly $20 billion on energy in fiscal 2011, making it the largest energy consumer in the country.

In addition, moving large volumes of fuel for military operations is costly and “entails logistical risks,” the Pentagon said in a 2011 report that found more than 3,000 Army personnel and contractors were wounded or killed from attacks on fuel and water supply and resupply convoys in Iraq and Afghanistan.

A soldier on a three-day foot patrol in Afghanistan may carry more than 33 batteries weighing up to 10 pounds to power radios, laptops, and other electrical gear, according to the report, which predicted such battery loads would increase to nearly 18 pounds in the future.

Burke’s position was created by Congress in 2009. Lawmakers concerned about the attacks on military fuel convoys wanted a senior official in charge of “operational energy,” defined by statute as “the energy required to train, move, and sustain forces, weapons, and equipment for military operations.”

Since then, the military has increased its focus on developing alternative fuels for jet fighters, warships and other military vehicles; replacing diesel generators with alternative energy systems; and increasing the efficiency of aircraft engines and lighting at military bases.

“The most powerful way for the Department of Defense to fix our energy challenge is to use less in the first place,” Burke said at the energy forum. “It’s not enough just to improve efficiency—we need to actually reduce the amount of fuel it requires to support forces.”