M-16s are stacked against sandbags prior to a training session at Fort Eustis, Va., Oct. 28, 2013. The Engagement Skills Trainer 2000 is a virtual, computer-based trainer that uses modified, retrofitted weapons to provide initial sustainment and advanced marksmanship with stationary and moving targets and reactionary-firing training. (U.S. Air Force photo by Staff Sgt. Ciara Wymbs/Released)