Today is the 148th anniversary of the Battle of South Mountain. After winning a decisive victory against US Major General John Pope’s Army of Virginia, at the Second Battle of Manassas, CSA General Robert E. Lee set his sights north of the Potomac River. His objectives were three fold: win a victory on Northern soil, potentially influencing the U.S. elections, remove the belligerents from war-torn Northern Virginia and lastly add disenfranchised Marylanders to his ravaged army with the hope of bringing Maryland into the Confederacy. After crossing the Potomac, Lee quickly realized that little Confederate sympathy existed in the central part of the state. Few men joined his army and the citizens showed little interest in supporting his efforts to liberate the state. More importantly, he found himself in a difficult tactical position. Headquartered in Frederick, Maryland, he quickly recognized that the Federal garrison at Harper’s Ferry posed a threat to his army. If he were to push west, or north, he invited attack from US Colonel Dixon S. Miles’ garrison. To alleviate the threat he sent Major General Thomas “Stonewall” Jackson’s wing to capture Harper’s Ferry. Leaving Major General Daniel Harvey “D.H.” Hill’s Division, along with some cavalry, to guard the passes at South Mountain, Lee pushed the rest of his Army of Northern Virginia towards Hagerstown.
Lee’s orders to his lieutenants, detailing the movement on Harper’s Ferry and the division of his army, would find their way to the commander of the Army of the Potomac, Major General George B. McClellan. The so called “Lost Orders” represented perhaps the largest security breach of the Civil War. General Orders 191 would reach McClellan after a soldier found the orders wrapped around three cigars near the Monocacy River. While the soldier inevitably believed the cigars to be a wonderful discovery, McClellan would be the ultimate beneficiary of the find. He knew that Jackson’s Wing was separated from CSA Major General James Longstreet’s Wing and that a small force, at South Mountain, was all that stood in his way to a potentially decisive victory against Robert E. Lee.
McClellan issued orders for a two pronged attack against the Confederate forces holding South Mountain on the evening of September 13. Major General William B. Franklin was to attack Crampton’s Gap at first light on the following morning. Once he had pushed the Confederate forces aside, he was to push south, down Pleasant Valley, to relieve Miles’ forces at Harper’s Ferry. Further north, at Fox’s and Turner’s gaps, the IX Corps, commanded by Major General Jesse Reno, and the I Corps, commanded by Major General Joseph Hooker, were to push through D.H. Hill’s Division the same morning. The Army of the Potomac was slow in moving and would face a much more daunting challenge than McClellan had foreseen. The delay in the engagement would cost many casualties – including General Reno. At the end of the day, Franklin held Crampton’s Gap and Major General Ambrose E. Burnside’s wing (I and IX corps) had only a badly mauled force in their front. After the fighting had ended, Lee recognized that the day had gone against him and ordered his army to reunite at Sharpsburg, Maryland – west of the banks of Antietam Creek. In the coming days, the opposing forces would meet and fight the largest single day battle, by casualties, in the history of the United States. While the engagements at South Mountain would pale against the upcoming Battle of Antietam, the results were sanguinary: 4,500 combined casualties.
There has been much written about the deliberate movements of McClellan after the discovery of Lee’s “Lost Orders.” Most scholars have been critical of how slowly he moved to attack Hill at South Mountain. However, in a recent interview with Tom Clemens, I learned that McClellan acted appropriately based on the information he had available to him on September 13. He had no solid intelligence on the size of the forces arrayed against him at South Mountain. Additionally, Frederick posed a problem for the movement of his large army – creating a 19th Century traffic jam. It took Lee a couple of days to move his smaller army through the city while it only took McClellan one day. While criticism can judiciously be piled on McClellan for his failure to act with alacrity on September 15, his movements against South Mountain were handled professionally.
For additional information refer to the following: