U.S. Air Force Col. Mark Nielsen addresses the troops after assuming command of the 307th Medical Squadron, April 12, 2015 at Barksdale Air Force Base, La Col. Nielsen is returning to the 307th Medical Squadron after working at the U.S. Air Force Academy as Individual Mobilization Augmentee to the United States Air Force Academy Command Surgeon and to the Commander of the 10th Medical Group for the past two years. (U.S. Air Force photo by Master Sgt. Laura Siebert/Released)