Tim Simmonds, an instructor with the 28th Security Forces Squadron, leads an active shooter brief inside the Installation Deployment Readiness Cell during an exercise at Ellsworth Air Force Base, S.D., Feb. 22, 2018. Ellsworth AFB conducted an active shooter exercise, testing Airmen in nearly 20 locations on their ability to respond to different situations in their buildings. (U.S. Air Force photo by Senior Airman Randahl J. Jenson)