U.S. Air Force Master Sgt. Scott Wagonblott, 633rd Communications Squadron information assurance manager, threatens first responders during an active-shooter exercise at Langley Air Force Base, Va., Nov. 19, 2013. Active-shooter exercises are used to test the response of units in the event of a real-world emergency. (U.S. Air Force photo by Airman Areca T. Wilson/Released)