U.S. Air Force Staff Sgt. Nicole Johnston, 633rd Security Forces Squadron NCO in charge of police services and confinement, took on the role of active shooter during an exercise at Joint Base Langley-Eustis, Va., Dec. 15, 2016. Johnston took action as the shooter after showing signs of irritation with customer service employees. (U.S. Air Force photo by Senior Airman Kimberly Nagle)