SAN ANTONIO (April 21, 2021) Master-at-Arms Seaman Apprentice Ashton Williams leads his unit while approaching a simulated active-shooter scenario during Master-at-Arms "A" school training on Naval Technical Training Center, Lackland Air Force Base in San Antonio, Texas. This training simulates scenarios involving armed suspects in a building. Master-at-Arms trainees learn how to infiltrate the hostile environment relying on team-based tactics to secure the area. Trainees wear shock vests that react to instructor-wielded mock weapons to mimic live-fire situations and make training more realistic. (U.S. Navy photo by Mass Communication Specialist 2nd Class J. Keith Wilson)