Airman 1st Class Jacob Hilley, 51st Security Forces Squadron member, acting as opposing forces, waits to fire on base defenders responding as reinforcements during exercise Vigilant Ace 16 at Osan Air Base, Republic of Korea, Nov. 5, 2015. Ground attacks on defensive fighting positions are a large part of testing the operational and tactical levels of coordination for the base. (U.S. Air Force photo/Staff Sgt. Amber Grimm)