 In that capacity, the 124th maneuvered on the field but did not participate in the Battle of South Mountain, as General Robert E. Lee began his advance into Maryland.The Twelfth Corps marched further into Maryland and, on September 17, 1862—less than six weeks after being commissioned—Clayton and the 124th Regiment were involved in the most violent one day conflict in American history—the Battle of Antietam.During Antietam, the 124th Regiment engaged in the furious fighting in Miller's cornfield.