WASHINGTON -- The Army is implementing ways to use energy more efficiently to protect Soldiers, conserve resources and enhance mission capabilities.

"Energy is mission critical. It is a vulnerability. It is a risk," said Katherine Hammack, assistant secretary of the Army for Installations, Energy and Environment.

"Right now, one in every 46 convoys in Afghanistan suffers a casualty," she said April 10, at a panel discussion on sustainable energy and national defense.

She told the audience at the George Washington University Law School that an estimated 20 percent of the casualties in Afghanistan occur during logistics resupply missions.

"It is a risk to our Soldiers as well as a risk to our operations," said Hammack.

"One key element in improving our energy security is to change our doctrine, change our materiel solutions, our policies and our procurement decisions to modify the way we use energy, while at the same time increasing mission capabilities," she said.

Hammack said the Army has taken energy-efficiency technologies and renewable energy projects into theater, including at remote forward operating bases that are resupplied through aerial missions.

She noted that in one remote post, Soldiers had to stop all operations, come down from the mountaintop and secure a safe area to receive an airdrop of supplies in what she described as a high-risk mission. But she said when the resources were conserved, those resupply missions happened less often, Soldiers stayed focused on operations instead of resupply, and assets could be deployed elsewhere.

Hammack said the Army has a program that encourages the private sector to install alternative energy on bases in the United States, and then the Army buys the energy. She described that as a "win-win" situation. Hammack said to date, the Army has secured about $1.5 billion in third-party investments on Army bases.

"We are ahead of the rest of the federal sector in using energy performance contracts," she said. "We are on track to meet our energy efficiency targets. We are on track to make our renewable energy projects and that is through leveraging the private sector interests -- not the taxpayer -- and paying for it out of existing budgets."

She said several Army bases are working toward being "Net Zero" in the areas of energy, water and waste by 2020.

"Technology and new techniques can work to make you more mission effective," she said. "It is a high priority to the Army to become less resource dependent, to increase our mission capabilities and increase our agility.

"We believe that what we're doing here can be models to communities, to cities, to universities, to other large areas where you have control over your infrastructure to better manage it so that it can be a better resource to the communities and the surroundings," she said.