The autumn of 1862 saw Robert E. Lee launch his first invasion of the North (American Civil War). On 5 September Lee’s army crossed the Potomac close to Leesburg, Virginia, with the intention of marching north through Maryland towards Pennsylvania. This plan was disrupted by the Union garrison of Harper’s Ferry. The town was defended by a force 12,000 strong, commanded by Colonel Dixon S. Miles. Miles did not have a great reputation, having been found drunk during the First Battle of Bull Run, and had presumably been posted to Harper’s Ferry in the expectation that it was a safe posting.
Lee had expected the garrison of Harper’s Ferry to be evacuated once his invasion began. However, General Halleck decided against this, arguing that possession of Harper’s Ferry was needed to secure the Baltimore and Ohio Railroad. This decision has often been criticized, on the grounds that it left the garrison vulnerable to capture. However, events were to show that this should not have been the case. One of Lee’s assumptions when he launched his invasion was that the Union army defeated at Second Bull Run was so badly mauled that it would take at least two weeks for it to begin to move against him. Instead, on 7 September, the same day that Lee’s army concentrated at Frederick, General McClellan led an army 85,000 strong out of their camps at Washington, and began a slow but steady march towards Lee.
At Frederick Lee remained unaware of this movement. His thoughts had now turned towards Harper’s Ferry. He was concerned that his lines of communication back into Virginia ran too close to the place for safety, and decided that he had to remove that threat before he could move north. He was quite convinced that he had more than enough time to split his army up, capture Harper’s Ferry, and reunite for the march north before McClellan was anywhere near.
Accordingly, on 10 September he dispatched two thirds of his army on an expedition against Harper’s Ferry. He remained with the other third, Longstreet’s Corps, which moved to Boonsborough, and then further north to Hagerstown, still in expectation of continuing north. Meanwhile, Stonewall Jackson was put in charge of a three pronged attack on Harper’s Ferry. The capture of the garrison presented a complex problem. Harper’s Ferry is located at the junction of the Potomac and Shenandoah Rivers, on the south side of the Potomac and the west side of the Shenandoah. If the garrison was not to escape, Jackson would have to block three possible escape routes – the overland route west, north over the Potomac and east over the Shenandoah. Accordingly, Lee dispatched three separate expeditions. Jackson was sent on the longest march. He was to march west, cross the Potomac upstream of Harper’s Ferry, then march back along the south bank of the river, cutting off the land route out of the town. A second force under General Walker was sent across the Potomac east of Harper’s Ferry, with orders to occupy Loudon Heights, east of the Shenandoah River. Finally, General McLaws was sent to occupy Maryland Heights, overlooking Harper’s Ferry from the north bank of the Potomac River.
Jackson’s march took four days. On 10 September he left Frederick, passed through Turner’s Gap in South Mountain, and camped near Boonsborough. On 11 September he crossed the Potomac at Williamsport, and camped four miles west of Martinsburg, with the intention of forcing the Union garrison there to retreat east into Harper’s Ferry. The next day he entered Martinsburg. Exactly as he hoped, the 2,500 strong garrison retreated to Harper’s Ferry. Finally, on 13 September Jackson reached Bolivar Heights, overlooking Harper’s Ferry from the west. On the same day McLaws and Walker both reached their destinations.
Maryland Heights quickly fell to McLaws. The Union defenders of the position abandoned the position without a serious fight, although it is not at all clear who was responsible for this move. It is clear that the few hundred men then on the Heights would easily have been brushed aside by McLaws’s men. Bolivar Heights was actively defended by the Union garrison, and remained at least partly in their position until the surrender.
14 September was largely wasted by the Confederate attackers. Communication between the three commands was not easy. It took most of the day for Jackson to gain a suitable position to bombard Harper’s Ferry. Finally, early on 15 September the Confederates began their bombardment, from all three sides. The bombardment lasted until 8.30 a.m. When it stopped, it was clear that the final assault would soon be launched. Colonel Miles decided that the situation was hopeless, and after a council of war the white flag was raised at 9.00 a.m. Unluckily for Miles, at that moment he was mortally wounded. His handling of the siege had been heavily criticised. His death removed the possibility that he could defend his decisions.
At Harper’s Ferry, Jackson captured 12,520 prisoners, 73 artillery pieces and a great deal of supplies. However, time was now short. McClellan had moved much faster than Lee had believed possible. On the same day that Harper’s Ferry fell, Lee was at Sharpsburg, with only three divisions to face the entire Army of the Potomac, which by the end of the day had more than enough men present along the Antietam Creek to have inflicted a very heavy defeat of Lee. Luckily for the Confederates, McClellan was not the man to launch such a daring attack. He took two more days to build himself up to attack Lee, finally launching that attack on 17 September (Battle of Antietam or Sharpsburg). By that time, most of Jackson’s men had rejoined Lee, arriving on 16 September. The final troops from Harper’s Ferry, under A.P. Hill, arrived during the battle itself, playing a crucial role in holding the Confederate line. The capture of Harper’s Ferry involved a much greater risk than Lee had believed when he had first decided to attempt it. Only McClellan’s lack of activity on 15 and 16 September saved Lee from suffering his first serious defeat.