U.S. Air Force Senior Airman Anthony Greene, 20th Security Forces Squadron (SFS) installation patrolman, advances on a simulated active shooter threat while Karl Johnson, 20th SFS trainer, observes at Shaw Air Force Base, S.C., Jan. 31, 2018. Greene was advancing slowly to maintain the element of surprise and avoid fatigue before engaging the simulated threat. (U.S. Air Force photo by Airman 1st Class Benjamin Ingold)