Air Force Staff Sgt. William Summerfield conducts an “outside the wire” perimeter check during Exercise Beverly Herd 17-1 at Osan Air Base, South Korea, March 1, 2017. Summerfield is a base defense operations center controller assigned to the 51st Security Forces Squadron, which maintains a secure environment to increase combat power during exercises and real-life scenarios. Air Force photo by Airman 1st Class Gwendalyn Smith