AERIAL SECURITY U.S. Marine Corps Gunnery Sgt. Marcus S. McCollum provides aerial security with a GAU-21 .50-caliber machine gun inside a CH-53E Super Stallion helicopter over Helmand province, Afghanistan, Aug. 22, 2013. McCollum, a crew chief, is assigned to Marine Heavy Helicopter Squadron 462. SHARE: Download: Full Size (0.06 MB) Credit: VIRIN: 960405-G-AUB78-734.jpg Photo Gallery