Today, September 14, is the 149th anniversary of the Battle of South Mountain. Part of the 1862 Maryland Campaign, it is more often than not overshadowed by the Battle of Antietam which followed three days later. With nearly 5,000 combined casualties, it is nonetheless a very significant battle.
Within days of CSA General Robert E. Lee’s victory over US Major General John Pope, at the Second Battle of Manassas (Bull Run), Lee would cross his Army of Northern Virginia into Maryland. Lincoln had just placed Major General George B. McClellan in command of the armies at Washington City (Potomac and Virginia). Lee, unable to strike a deadly blow to Pope’s retreating army after the Battle of Chantilly, believed it essential that he maintain the momentum his army achieved after the Seven Days battles and Second Manassas. His plan called for a movement to the Frederick area where he could await the Federals on a field of his own choosing. Unfortunately, US Colonel Dixon S. Miles’ garrison at Harper’s Ferry posed a threat to the rear of his army. Additional Federal troops near Martinsburg, Virginia (present day West Virginia) could sever his supply line – effectively crippling the entire campaign. With roughly 60,000 soldiers in his army, he was severely outnumbered by whatever combined army the U.S. War Department sent to pursue him. Simply put, Lee found himself in a very precarious position.
In an audacious move, believing the Union troops would be slow in pursuit, Lee separated his army sending Major General James Longstreet’s command through Boonsboro to Hagerstown, Major General Thomas “Stonewall” Jackson’s command to capture Harper’s Ferry and leaving a portion of his cavalry, and Major General Daniel Harvey (D.H.) Hill’s division, to guard the passes in South Mountain, just west of Frederick. Putting his plan in motion, Lee issued Special Order 191 sending copies to Jackson, Longstreet, two division commanders (Lafayette McLaws and D.H. Hill) and cavalry commander, Major General J.E.B. Stuart. The armies were to move at first light on September 10.
McClellan would arrive in Frederick with the Army of the Potomac on September 13. His army would be met with cheers from the largely loyal population of central Maryland. While resting near the Monocacy River, a misplaced copy of Lee’s Special Order 191 would be found wrapped around three cigars by a soldier in the 27th Indiana Volunteer Infantry. Believing it significant, the soldier passed it to his commander where it would make its way to McClellan.
While McClellan would immediately notify President Lincoln of his find, explaining “no time would be lost” in taking advantage of the most important intelligence of the war, it would take time to get his massive army through Frederick. Orders were issued to his senior lieutenants, major generals Ambrose E. Burnside and William B. Franklin, to move with alacrity at first light, September 14. Burnside was to push towards the northernmost gap, Turner’s, on the National Road. He was to clear the gap and push after Longstreet’s command. Mclellan’s orders to Bill Franklin were explicit and detailed, believing his role crucial to rescuing Miles’ garrison at Harper’s Ferry. He was to waste no time pushing through Burkittsville before first light, and using the Gapland Road, force his way through Crampton’s Gap. Once the gap was cleared he was to enter Pleasant Valley and march south toward’s Maryland Heights, relieving Miles. Unfortunately, the timing was not achieved and precious time would be lost reaching the gap.
The Battle of South Mountain was crucial for each army commander. Lee needed to delay any incursion into Pleasant Valley to provide Jackson time to consummate the capture of Harper’s Ferry. If McClellan did not push through the gaps quickly, Harper’s Ferry would eventually fall and any hope of defeating Lee piecemeal would vanish. The fate of both armies hinged on the defense which D.H. Hill could muster at the gaps. Lee’s Maryland Campaign and the future of the Union hung in the balance.
To read my complete essay on the Battle of South Mountain, click HERE.
To listen to a recent interview I had with Dr. Tom Clemens, editor of “The Maryland Campaign of September 1862, Vol. 1: South Mountain,” click HERE.
To view a short photo essay on South Mountain, click HERE.