633rd Civil Engineer Squadron firefighters place Airman 1st Class Mark Reposar, 1st Operations Support Squadron air traffic control apprentice, on to a stretcher during an active shooter exercise at Langley Air Force Base, Va., Dec. 8, 2011. Langley AFB conducted the full-scale exercise for assigned units and agencies to exercise plans, checklists, and standard operating procedures. (U.S. Air Force photo by Airman 1st Class Kayla Newman/Released)