U.S. Marine Corps Lance Cpl. Justin P. Ruff, bottom

U.S. Marine Corps Lance Cpl. Justin P. Ruff, bottom left, automatic rifleman, Charlie Company, 1st Battalion, 6th Marine Regiment, 2nd Marine Division (MARDIV), receives instructions on remedial action and clearing of a M249 squad automatic weapon system during down time before the start of Mountain Exercise 5-15 at the Marine Corps Mountain Warfare Training Center, Bridgeport, Calif., Sept. 4, 2015. Marines participate in a month-long field exercise focusing on core mission essential tasks such as assault climbing, animal packing and small unit movements, to strengthen expeditionary high altitude warfare tactics in a mountainous environment against a hybrid threat, as they prepare for world-wide deployment. (U.S. Marine Corps photo by Cpl. Kelly L. Street, 2D MARDIV COMCAM/Released)