From the Peninsula to Maryland: Jackson's role in the summer of 1862
Jackson often played the role of the audacious "hammer" of the army of Northern Virginia, taking quick and assertive offensive action. His roles in the Northern Virginia Campaign of August 1862, however, were an interesting blend of hammer (offensive) and anvil (defensive). Sent north to disrupt John Pope's oppressive treatment of the people of Northern Virginia, Jackson successfully executed a sweeping flanking maneuver that placed his command in the rear of Pope's Army of Virginia. From this position he successfully captured the Union Army depot and all of the supplies at Manassas Junction before taking up a defensive position and effectively inviting Pope to assault him.
Pope obliged and for two days (August 28-29), Pope pounded Jackson as Longstreet and the remainder of the army marched north to reach the battlefield. Jackson held out despite delays in getting Longstreet's troops into action, even when his men were reduced to hurling rocks when they ran out of ammunition. This allowed for Longstreet to launch "the largest, simultaneous mass assault of the war" on August 30, sending more than 28,000 men into the left flank of the Union army.
When Lee decided to cross the Potomac and invade the North in the Maryland Campaign, he had intended to push toward Baltimore, Washington, or Pennsylvania, but became concerned about the Union presence in and near Harpers Ferry. In Special Orders 191 Lee sent Jackson to capture Harpers Ferry, which he accomplished on September 15. Jackson then pushed his men to join the rest of the army at Sharpsburg, Maryland.
Jackson arrived in time to bear the brunt of the Federal advances on the northern end of the battlefield in the morning phase of the Battle of Antietam on September 17. Just as it looked like the battle would be lost when Burnside's men began to turn the right of the Confederate line, A.P. Hill, leading the last elements of Jackson's Corps, arrived on the field from Harpers Ferry and stopped the Federal Advance.
Following the battle Jackson was promoted to Lieutenant General and his command redesignated as the Second Corps on October 10.