Marines fire an M777 towed 155 mm howitzer during an exercise as part of a weapons and tactics course for instructors at Fire Base Burt, Calif., April 17, 2017. The course emphasizes the operational integration of the six functions of Marine Corps aviation to support a Marine Air Ground Task Force. The Marines are assigned to 1st Battalion, 10th Marine Regiment. Marine Corps photo by Lance Cpl. Clare J. Shaffer