Marine Corps Air Facility Quantico personnel from Marine, Antietam National Battlefield

Marine Corps Air Facility Quantico personnel from Marine Corps Base Quantico, Va., look over the Burnside Bridge during a hike in Antietam National Battlefield, Sharpsburg, Md., April 24, 2015. The hike and battlefield study was part of a professional military education and unit cohesion-building event. The Battle of Antietam was the first invasion of the North by Confederate troops during the civil war and the bloodiest one-day battle in American history. By 1 p.m., Sept. 17, 1862, Maj. Gen. Ambrose E. Burnside and his troops, who had been fighting to cross the Antietam Creek since the morning, finally pushed the Confederates back across the bridge and up towards Sharpsburg, Md.