On the 15th, after a brief engagement, the garrison at Harper's Ferry surrendered.
Meanwhile, on September 13th, General McClellan had reached Frederick, and it was there, by a strange accident, constituting one of the pivots upon which the result of the war seemed to turn, that he came into possession of a copy of General Lee's order, and was so made aware of the division of our army and of the comparatively small force that confronted him. His movements, so very slow up to this time, were greatly accelerated. In his report he says, ‘Upon learning the contents of this order, I at once gave orders for vigorous pursuit.’
General Longstreet, with nine brigades, was now at Hagerstown, and General D. H. Hill, with five brigades, was at Boonsborough guarding the pass through South Mountain and immediately confronting the Federal army. General McClellan moved promptly on the morning of September 14th to force a passage here, and sent Franklin's Corps to intercept the movements of General McLaws, whose position, until the capture of Harper's Ferry, was one of great peril.
According to General D. H. Hill's official report, the strength of his division at this time was less than 5,000 men. For six or seven hours this force at South Mountain pass resisted the assaults of two corps of General McClellan's army. At about 3 o'clock P. M. General Hill was re-enforced by the brigades of Drayton and Anderson, and later in the day he was joined by General Longstreet, with the brigades of Pickett, Kemper, Jenkins, Hood, Whiting and Evans; only four of these, however, numbering about 3,000 men, became seriously engaged. Thus it will be seen that a force of less than 10,000 men resisted the assaults of two corps of the Federal army and held General McClellan in check for an entire day. General McClellan in his report states that he had 30,000 men in this encounter.
While General Hill was thus hotly engaged at Boonsborough pass, General McLaws was being pressed at Crampton Gap by General Franklin, in command of the force sent by General McClellan to overwhelm him and prevent his rejoining General Lee. The commands engaged in these encounters with the enemy were, of course, seriously reduced.
