Senior Airman John Halligan, 28th Security Forces Squadron response force leader, scans a facility for threats during an active shooter training exercise in a shoot house at Ellsworth Air Force Base, S.D., Aug. 24, 2012. The course focused on preparing Defenders to rapidly respond and deploy to an active shooter scenario, eliminate the threat, and prevent harm to innocent people nearby. (U.S. Air Force photo by Airman 1st Class Hrair H. Palyan/Released)