Irvin McDowell, responsible for the left wing of Pope’s army, finished his orders shortly after midnight and sent them to the division commanders of his own corps and of Franz Sigel’s corps. Pope planned to trap Jackson’s Wing of the Confederate Army of Northern Virginia at Manassas Junction, separating it from Longstreet’s Wing still in the Valley and smashing it against Bull Run. McDowell was responsible for bringing the over 20,000 men he had stretched from Warrenton to Warrenton Junction west, following two corps led by Sam Heintzelman; two waves crashing onto the Stonewall only a few miles south of his greatest triumph.
To accomplish this, McDowell ordered Sigel’s First Corps, Army of Virginia to march straight on Manassas Junction, his right-most brigades marching on the Orange and Alexandria Railroad. Sigel’s men were to be augmented by John F. Reynolds’ Pennsylvania Reserves from his own Third Corps, Army of Virginia on the left, marching down the Warrenton Turnpike [US 29]. Sigel plus Reynolds would form a giant squeegee, sweeping any Rebels in front of them.
McDowell’s other two divisions were to follow the turnpike as well. Rufus King, who had not been confined to an ambulance since his seizure at Rappahannock Station about two weeks earlier, nonetheless was given the responsibility of guarding the flank, by deploying his men north of the Turnpike for the march. With their leader confined to bed, McDowell decided to make his personal headquarters with his old division.
James Ricketts, commanding the final division for McDowell, was to follow along the Turnpike in reserve as far as Gainesville, where he would determine if Longstreet’s Wing was attempting to cross through Thoroughfare Gap. If so, he would go relieve the cavalry units watching the Gap. If not, he would move into position to King’s left and act as a cork for any of Jackson’s forces that might think they could escape the bottle Pope planned to put them in.
Issued as General Orders No. 10, McDowell sent off the orders and, predictably, they immediately went awry. Sigel either couldn’t or wouldn’t get his men moving in time, and Reynolds’ fumed while dawn broke, and the sun rose in the sky with no movement made.
West of Thoroughfare Gap
Robert E. Lee had left Salem in Page County before dawn and rode with his staff towards White Plains [The Plains], where he would meet with James “Pete” Longstreet. By afternoon they hoped to have Longstreet’s wing of the army through Thoroughfare Gap, where it could join with Jackson’s to confront Pope.
With Hooker’s division bloodied from the day before [at Kettle Run], Sam Heintzelman started Phil Kearny’s division first up the O&A Railroad towards Manassas Junction, he and John Pope riding along. Not surprisingly, Kearny stepped off exactly on time, with Hooker close behind him.
Jackson’s men had spent a busy night. The encounter with Hooker the day before had alerted him that he had run out of time for raiding, and it was time for the battle. But Pope had pursued with more skill than Stonewall had expected, and his divisions were in poor position for a fight.
Jackson decided to move north of the Warrenton Turnpike [US 29], the ideal position to meet a force marching from Manassas Junction while being reinforced from Thoroughfare Gap. Ewell’s Division was already almost there, having pulled back to the Manassas Gap Railroad after fighting with Hooker at Kettle Run.
The supplies he couldn’t carry with him, Jackson torched around midnight, and began marching with his division, under the leadership of William Taliaferro, up the Sudley Road to take up position at the old battlefield, perhaps to gain inspiration. A.P. Hill’s Light Division, along with Fitzhugh Lee’s brigade of cavalry, he sent north on the Centreville Road, with orders to destroy the O&A track east of that town, to prevent Pope’s reinforcement by McClellan from Alexandria.
Jesse Reno’s Ninth Corps was adjusting to command under Pope. They started their move down what is today (more or less) Vint Hill Road to Bristoe Station, reaching the sight of the fight on August 27 not long after Heintzelman had vacated it, and following them up the O&A.