Staff Sgt. Michael Gwin, a military working dog handler assigned to the 28th Security Forces Squadron, runs Rex, a military working dog assigned to the 28th SFS, through an obstacle course at Ellsworth Air Force Base, S.D., Oct 9, 2015. MWD’s undergo constant training to ensure they are fit to fight anytime anywhere. (U.S. Air Force photo by SrA Rebecca Imwalle)