Staff Sgt. James Matthews II, 81st Security Forces Squadron flight sergeant, holds his post during an active shooter exercise at the Larcher Chapel Sept. 21, 2017, on Keesler Air Force Base, Miss. The exercise simulated an active shooter at the Arnold Medical Annex and the Larcher Chapel in order to test the base's ability to respond to and recover from a mass casualty event. (U.S. Air Force photo by Kemberly Groue)