The U.S. Department of Defense consumes a lot of energy - close to 80% of the total used by the entire federal government. The primary sink is aviation. Almost 48% of the energy consumed by the government is in the form of jet fuel, and 98.6% of that jet fuel is used for defense.

Data source: http://www.eia.gov/totalenergy/data/annual/showtext.cfm?t=ptb0113