As seen through a night-vision device, U.S. Marine Corps Gunnery Sgt. Michael Kelly, left, instructs U.S. Marine Corps Lance Cpl. Kirk Goldsmith on proper air-to-ground observation techniques while conducting a tail gun live-fire exercise in Southwest Asia, Dec. 20, 2015. Kelly and Goldsmith are assigned to Marine Medium Tiltrotor Squadron 268, Special Purpose Marine Air-Ground Task Force-Crisis Response-Central Command. U.S. Marine Corps photo by Lance Cpl. Clarence Leake