Battle of South Mountain was a Civil War engagement fought in Maryland, 1862. It was a Union victory.
The Battle of South Mountain, known in several early Southern accounts as the Battle of Boonsboro Gap, was fought on September 14, 1862, as part of the Maryland campaign of the American Civil War. Three pitched battles were fought for possession of three South Mountain passes: Crampton's, Turner's, and Fox's Gaps.
Maj. Gen. George B. McClellan, commanding the Union Army of the Potomac, needed to pass through these gaps in his pursuit of Confederate General Robert E. Lee's precariously divided Army of Northern Virginia.
Although the delay bought at South Mountain would allow him to reunite his army and forestall defeat in detail, Lee considered termination of the Maryland Campaign at…
On September 14, 1862, Union and Confederate forces clashed at South Mountain, a fight that early Southern accounts sometimes called the Battle of Boonsboro Gap. This engagement formed part of the Maryland campaign during the American Civil War. Fighting broke out at three separate mountain passes as both sides sought control of Crampton's, Turner's, and Fox's Gaps, resulting in three distinct pitched battles.
For Maj. Gen. George B. McClellan, leading the Union Army of the Potomac, controlling these gaps was essential to his efforts to catch up with Confederate General Robert E. Lee, whose Army of Northern Virginia had been split into vulnerable segments. The time McClellan's forces spent securing South Mountain ultimately gave Lee the chance to bring his scattered units back together and avoid being beaten piecemeal. Even so, by the time night fell, Lee was weighing whether to end the Maryland Campaign altogether.
Once the Blue Ridge Mountains cross into Maryland, they continue under a different name: South Mountain. This ridge forms a natural barrier standing between the eastern portion of Maryland and the valleys of Hagerstown and Cumberland.
Lee's push into Maryland took an unexpected turn when McClellan's men recovered a written copy of his battle plan, Special Order 191, which laid out where Confederate troops were headed. This document revealed to McClellan that Lee had divided his army, dispatching Maj. Gen. Thomas J. Jackson and part of his force to besiege Harper's Ferry while the remainder camped near Boonsboro under Maj. Gen. James Longstreet's command. Lee's strategy called for securing his rear by capturing Harper's Ferry, then pressing forward into Union territory, destroying the Monocacy aqueduct along the way, before setting his sights on Baltimore, Philadelphia, or Washington, D.C.
Responding to this threat, McClellan pushed the Army of the Potomac westward, hoping to strike Lee's scattered units before they could reunite.
For the assault on the mountain passes, McClellan split his army into three temporary wings. Maj. Gen. Ambrose Burnside led the Right Wing, made up of the I Corps under Maj. Gen. Joseph Hooker and the IX Corps under Maj. Gen. Jesse L. Reno, and this wing moved toward Turner's Gap and Fox's Gap to the north. To the south, Maj. Gen. William B. Franklin directed the Left Wing toward Crampton's Gap, bringing his VI Corps along with Maj. Gen. Darius N. Couch's division from the IV Corps. Meanwhile, Maj. Gen. Edwin Vose Sumner held the Center Wing, comprising the II Corps and XII Corps, back in reserve.
Earlier, Lee had ordered Longstreet's column north from Boonsboro to counter what appeared to be a Pennsylvania-based threat. Once word reached him that McClellan had gained access to his plans, Lee moved quickly to summon Longstreet back, hoping to bolster defenses at the South Mountain passes and stall McClellan's progress. By the time fighting broke out, the only Confederate troops remaining near Boonsboro belonged to Maj. Gen. D.H. Hill's division, which consisted of five brigades.
The 23rd Ohio Infantry counted among its ranks two men who would later occupy the nation's highest office. Rutherford B. Hayes led the regiment as commander, while William McKinley served under him as commissary sergeant, and both saw action at Fox's Gap during the Battle of South Mountain. By the war's close, Hayes had risen to brevet major general, and McKinley had attained the rank of brevet major. Two decades apart, each man would go on to win election as president, Hayes in 1876 and McKinley in 1896.
As evening fell, Lee recognized that Crampton's Gap had slipped away and that his hold on Fox's and Turner's Gaps could not last. He gave the order for his smaller force to pull back from South Mountain. This left McClellan positioned to crush Lee's army before its scattered pieces could come together. Of the 28,000 Union troops involved, 2,325 became casualties, including 443 dead, 1,807 wounded, and 75 missing. The Confederates, numbering 18,000, suffered 2,685 losses, with 325 killed, 1,560 wounded, and 800 unaccounted for.
For the Army of the Potomac, worn down by prior setbacks, this fight at South Mountain provided a much needed lift in spirits. The New York World declared that the clash had reversed the momentum of rebel victories, insisting that the rebels' strength had been broken beyond repair. Lee, for his part, began to consider whether his campaign into Maryland had reached its conclusion.
Yet McClellan failed to press his advantage on September 15, doing little despite his success at South Mountain. This hesitation sealed the fate of the Union garrison at Harpers Ferry, which fell into Confederate hands, and it also bought Lee the time he needed to bring his separated divisions together at Sharpsburg, setting the stage for the Battle of Antietam on September 17.
Units recorded as engaged in the compiled order of battle.
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