On September 17, 1862, the single bloodiest day of the Civil War, the Army of the Potomac under George B. McClellan clashed with Lee's invading Army of Northern Virginia at Antietam Creek. General Francis W. Palfrey (1831--1889), then lieutenant colonel of the 20th Massachusetts and later a founding member of the Military Historical Society of Massachusetts, was severely wounded in the savage struggle that forced the Confederates to retreat across...