The Battle of South Mountain

On the morning of September 14, Major General George B. McClellan’s Federal Army of the Potomac began moving to confront General Robert E. Lee’s divided Confederate Army of Northern Virginia in Maryland. This movement came 18 crucial hours after McClellan had received the “lost order” describing the exact positions of the enemy units and how they were dangerously spread out in Maryland and northwestern Virginia. McClellan organized the six corps of his army into three wings for the westward advance:

  • The right (i.e., northern) wing was commanded by Major General Ambrose E. Burnside. It consisted of Major General Joseph Hooker’s First Corps and Major General Jesse Reno’s Ninth Corps.
  • The left (i.e., southern) wing was commanded by Major General William B. Franklin. It consisted of his Sixth Corps and elements of Major General Darius Couch’s Fourth Corps.
  • The center was commanded by Major General Edwin V. Sumner. It consisted of his Second Corps and Major General Alpheus Williams’s Twelfth Corps. McClellan kept this element of his army, along with Major General Fitz John Porter’s Fifth Corps, as his reserve.

Lee’s army was divided into four main sections:

  • Major General James Longstreet’s command was moving north from Hagerstown, Maryland, to face a potential threat from the volunteers being raised in Pennsylvania.
  • Major General Thomas J. “Stonewall” Jackson’s command was moving on the Federal garrison at Harpers Ferry in Virginia.
  • Major General J.E.B. “Jeb” Stuart’s cavalry operated in and around the South Mountain region.
  • Major General D.H. Hill’s division of five brigades was moving from Boonsboro, Maryland, to guard the vital passes through South Mountain, a section of the Blue Ridge chain about 20 miles south of the Pennsylvania border.

There were three mountain passes: Turner’s Gap to the north, Fox’s Gap in the center, and Crampton’s Gap to the south. McClellan planned to storm through Hill’s small force with four corps, seize the mountain passes, and from there “cut the enemy in two and beat him in detail.” McClellan rode down the National road to Middletown and watched his men march past on their way into battle. According to a Massachusetts solder:

“It seemed as if an intermission had been declared in order that a reception might be tendered to the general-in-chief. A great crowd continually surrounded him, and the most extravagant demonstrations were indulged in. Hundreds even hugged the horse’s legs and caressed his head and mane. While the troops were thus surging by, the general continually pointed with his finger to the gap in the mountain through which our path lay. It was like a great scene in a play, with the roar of the guns for an accompaniment.”

Lee, surprised by the sudden acceleration of McClellan’s advance, learned from Stuart that McClellan knew his plans. He hurriedly called on Longstreet to turn about and reinforce the Confederates at South Mountain. Hill watched the massive blue columns of some 30,000 men moving toward him with deadly intentions and later admitted that he had never felt so alone as on this day.

To the north, Burnside was in command, but Reno suggested making a diversionary attack on Turner’s and Fox’s gaps while Franklin attacked Crampton’s. McClellan’s aide replied, “General McClellan desires you to comply with this request,” and put Reno in charge of carrying it out. Action began around 9 a.m. when Brigadier General Jacob D. Cox’s Kanawha Division of Reno’s corps attacked Confederates in the pastures in front of Fox’s Gap.

The Federals attempted a flank attack, in which Lieutenant Colonel (and future U.S. President) Rutherford B. Hayes of the 23rd Ohio was wounded. Cox’s Federals reached the crest of the gap but had to stop there due to exhaustion. Confederates led by Brigadier General Samuel Garland, Jr., poured into the gap and counterattacked; Garland was killed in action.

Reno committed the rest of his corps on a final push, and he rode up to personally direct the assault. Reno was wounded and brought to the rear, where he was met by Brigadier General Samuel Sturgis. Reno told him, “Hallo, Sam, I’m dead!” Sturgis told him the wound was not that bad, but Reno insisted, “Yes, yes, I’m dead. Good bye!” Reno died soon after.

Reno was the third Federal general to be killed in action in the past two weeks (Philip Kearny and Isaac Stevens had been killed at Chantilly on the 1st). Brigadier General John Gibbon, commanding the Iron Brigade, later wrote his wife, “Poor Reno was shot right through the body and lived only a short time. It is said the bullet went directly thro’ his wife’s likeness which he had hung around his neck.”

The Federals captured most of Garland’s brigade, but their assault on Fox’s Gap stalled in the face of stubborn resistance and the arrival of Confederate reinforcements under Brigadier General John Bell Hood.

The Battle of South Mountain | Image Credit:

Farther north, Hooker’s three divisions advanced on the National road in Boonsboro to seize Turner’s Gap, a mile above Fox’s. Confederate defenders resisted into the afternoon, but superior Federal numbers eventually overwhelmed them. As the Confederates began to break, two of Longstreet’s divisions arrived to reinforce them and prevent a rout. Fighting continued until the Federals secured the high ground at Turner’s around 10 p.m. But the Confederates still held the gap.

To the south, Franklin had 12,000 men against less than 1,000 Confederates at Crampton’s Gap. McClellan had directed Franklin to break through the pass and “cut off, destroy or capture (Major General Lafayette) McLaws’ command & relieve Col (Dixon) Miles” at Harpers Ferry, just a few miles away. But being the deliberate officer that he was, Franklin spent three hours arranging his men to carry out those orders. A Confederate noted that the Federals looked like “a lion making exceedingly careful preparations to spring on a plucky little mouse.”

A single Confederate brigade under Colonel William A. Parham guarded the gap when the Federals attacked around noon. The Confederates held against repeated attacks for several hours, but they eventually wavered and broke. Brigadier General Howell Cobb arrived with Confederate reinforcements, but they soon wavered as well and joined the panicked retreat down the mountainside into Pleasant Valley. The Federals took 400 prisoners, mostly from Cobb’s late-arriving units.

The arrival of McLaws and his men from Harpers Ferry finally stabilized the Confederate line. Franklin proudly wrote his wife that this was “one of the prettiest fights of the war & I arranged the details myself.” But it could have been so much more. Unaware that his troops could easily destroy the enemy, Franklin called a halt and camped for the night, missing a prime opportunity to relieve the Harpers Ferry garrison and cripple Lee’s army.

The battle ended in Federal victory, but the Confederates had held the mountain passes for most of the day against a force five times their size. This gave Lee the time he needed to concentrate his army. The Federals sustained 2,325 casualties (443 killed, 1,807 wounded, and 75 missing) out of about 28,000 effectives. The Confederates lost 2,685 (325 killed, 1,560 wounded, and 800 missing or captured) from some 18,000.

“It was a glorious victory,” McClellan reported to General-in-Chief Henry W. Halleck. He said he expected Lee to either fall back or “appear in increased force in the morning. I am hurrying up everything from the rear to be prepared for any eventuality.” To his wife Ellen, McClellan wrote on the 15th, “We yesterday gained a glorious & complete victory; every moment adds to its importance.” The fight at South Mountain provided a much-needed boost to Federal morale. According to the New York World, this action stemmed “the tide of rebel successes… the strength of the rebels is hopelessly broken.”

Confederates doubted these Federal claims of complete victory. The Federals did ultimately drive the Confederates off and seize control of the mountain passes, but they did not capitalize on Lee’s “lost order” by destroying his army while it was still divided. This prompted D.H. Hill to assert that if the battle “was fought to save Lee’s trains and artillery, and to reunite his scattered forces, it was a Confederate success.”

When Lee received news of the fight at South Mountain, he decided to return to Virginia. Word of Federals taking Crampton’s Gap and threatening McLaws’s rear at Harpers Ferry confirmed Lee’s decision. He withdrew his men from South Mountain during the night and sent a message to McLaws: “The day has gone against us and this army will go by Sharpsburg and cross the (Potomac) river.”

Lee sought to concentrate his army at Sharpsburg, the first stop on his withdrawal, about six miles west of South Mountain. But news from “Stonewall” Jackson at Harpers Ferry soon compelled Lee to change his mind and make a stand.


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