Senior Airman Eric Ackerberg, 11th Civil Engineer Squadron firefighter, ties a Prusik knot around a single rope during the final evaluation of the 15-day Department of Defense Rescue Technical Course on Joint Base Andrews, Md., Nov. 3, 2015. The course taught the 11th CES firefighters the techniques and skills of how to tie any knot needed for multiple rescue scenarios covered in the 15-day course. (U.S. Air Force photo by Airman 1st Class Philip Bryant/Released)