U.S. Air Force Staff Sgt. William McDonald, 51st Civil Engineer Squadron material control craftsman and 51st Security Forces Squadron augmentee, mans a defensive fighting position during exercise Vigilant Ace 18 at Osan Air Base, Republic of Korea. As they would during a real-world situation, the 51st SFS augmentees are bolstering Osan’s defense forces manning DFPs and aiding in patrols during VA18. (U.S. Air Force photo by Staff Sgt. Alex Fox Echols III)