U.S. Air Force Tech. Sgt. Justo Scott, 633rd Security Forces Squadron flight chief, takes aim at a gunman during an active shooter exercise at Langley Air Force Base, Va., Dec. 8, 2011. The exercise helped to prepare 633rd Air Base Wing personnel for future exercises and potential real-world situations. (U.S. Air Force photo by Staff Sgt. Antoinette Gibson/Released)