Marines with Battery I, 3rd Battalion, 11th Marine Regiment, 1st Marine Division, fire an M777 Howitzer during the opening day of live-fire operations for Steel Knight at Marine Corps Air Ground Combat Center Twentynine Palms, California, on Dec. 10, 2015. The tough, realistic training is intended to develop combat skills necessary to operate as the ground combat element of the I Marine Expeditionary Force. (U.S. Marine Corps photo by Cpl. Cameron Storm)