On 14 September 1862 the Union Army of the Potomac under Major General George B. McClellan attacked the Confederate troops holding the three gaps of South Mountain in Maryland: Crampton's, Fox's and Turner's. McClellan knew where to strike because his soldiers had found a lost copy of Robert E. Lee's orders the day before. By nightfall the Union held the passes, but the Confederate defense had bought Lee the time he needed to pull his scattered army together at Sharpsburg, where the bloodiest day of the war was fought three days later.
Three cigars and a lost order
In early September 1862 Lee carried the war into Maryland. In Special Order 191 he divided his army, sending Stonewall Jackson to capture the Union garrison at Harpers Ferry while the rest marched on. On 13 September, the American Battlefield Trust writes, Corporal Barton W. Mitchell and First Sergeant John M. Bloss of the 27th Indiana found a copy of the order wrapped around three cigars in a field outside Frederick. It reached McClellan before noon, and by nightfall he had ordered the army to move west at dawn against the South Mountain passes. The National Park Service sums it up: mislaid communications led to the battle.1
Lee learned of the danger that night and ordered General James Longstreet back to Boonsboro to support General D. H. Hill, whose division of about 5,000 men was all that guarded Fox's and Turner's Gaps, with J. E. B. Stuart's cavalry.2
The fight for the gaps
The first shots were fired near Fox's Gap on the morning of 14 September. There the Confederate brigade of General Samuel Garland stood in the path of the attack, and Garland was mortally wounded, the moment the lithograph above sets out to show. The Union IX Corps at Fox's Gap was commanded by General Jesse L. Reno, while Ambrose Burnside led a wing of the army. Reno was also killed: the Stone Sentinels battlefield guide says he was mortally wounded by friendly fire in the darkness at the end of the fighting, and his monument at the summit of Fox's Gap marks the spot.3
Fighting went on all day at Fox's and Turner's Gaps as Longstreet's men came up, and farther south there was fighting at Crampton's Gap as well. The American Battlefield Trust estimates about 28,000 Union and 18,000 Confederate soldiers engaged. By nightfall the Union held the passes, and Lee withdrew his outnumbered forces; the Confederates were gone by sunrise on 15 September.4
Three days to Antietam
The American Battlefield Trust estimates the Union losses at 2,325 killed, wounded and missing and the Confederate losses at 2,685, including 800 missing or captured. Frederick Dyer's Compendium of the War of the Rebellion, published by the National Park Service, lists Union losses of 1,813 at South Mountain and 533 at Crampton's Gap, a total of 2,346.5
The day was a Union victory, but the National Park Service notes that the Confederate resistance let Lee reunite and concentrate his army for the Battle of Antietam three days later. Harpers Ferry surrendered to Jackson on 15 September, and on 17 September the two armies met along Antietam Creek near Sharpsburg. That battle, America's bloodiest single day, is told in our article on Antietam.6
