Battle of South Mountain
South Mountain, Maryland, USA
What happened
The Union Army of the Potomac under George B. McClellan fought Confederate troops of Robert E. Lee's army, including D.H. Hill's division. Union soldiers had found a lost copy of Lee's plans, called Special Order 191, which showed that his army was split into parts. McClellan's troops pushed west to force their way through three mountain passes: Crampton's, Turner's and Fox's Gaps. The Union broke through at Crampton's Gap, while the Confederates held the other two gaps for the day before Lee pulled back.
Why it matters
The lost order gave McClellan a rare chance to catch Lee's army while it was divided. McClellan is often criticized for waiting 18 hours before acting on it, which gave Lee time to gather his scattered troops.
What came next
Lee ordered his troops to Sharpsburg, where the two armies met at Antietam on 17 September 1862.
Did you know?
Two future presidents, Rutherford B. Hayes and William McKinley, fought at Fox's Gap with the 23rd Ohio.
Timeline
- 13 Sep 1862Union soldiers at Frederick find a copy of Special Order 191.
- 12–15 Sep 1862Stonewall Jackson captures Harpers Ferry.
- 14 Sep 1862Battle of South Mountain.
- 17 Sep 1862Battle of Antietam.