Staff Sgt. William Summerfield, a 51st Security Forces Squadron base defense operations center controller, conducts an “outside the wire” perimeter check during Exercise Beverly Herd 17-1 at Osan Air Base, Republic of Korea, March 1, 2017. The 51st SFS’s mission is to maintain a secure environment and to increase combat power during exercise and real life scenarios. (U.S. Air Force photo/Airman 1st Class Gwendalyn Smith)