Editing First Battle of Bull Run (section)

=== McDowell's plan and initial movements in the Manassas Campaign ===
On July 16, McDowell departed Washington with the largest field army yet gathered on the [[North America]]n continent, about 35,000 men (28,452 effectives).<ref name=strength>Strength figures vary by source. Eicher, pp. 87–88: 35,000 Union, 32,000 Confederate; Esposito, map 19: 35,000 Union, 29,000 Confederate; [http://www.history.army.mil/StaffRide/1st%20Bull%20Run/Organization.htm Ballard] {{Webarchive |url=https://web.archive.org/web/20090101155707/http://www.history.army.mil/StaffRide/1st%20Bull%20Run/Organization.htm |date=January 1, 2009 }}, 35,000 Union (18,000 engaged), 34,000 Confederate (18,000 engaged); Salmon, p. 20: 28,450 Union, 32,230 Confederate; Kennedy, p. 14: 35,000 Union, 33,000 Confederate; Livermore, p. 77: 28,452 Union "effectives", 32,323 Confederate engaged. Writing in ''[[The Century Magazine]]'', adjutant generals [[James Barnet Fry|James B. Fry]] [http://www.rugreview.com/cw/cwcu.htm cites] {{webarchive |url=https://web.archive.org/web/20080509094034/http://www.rugreview.com/cw/cwcu.htm |date=May 9, 2008 }} 18,572 Union men (including stragglers not on the field) and 24 guns engaged, [[Thomas Jordan (general)|Thomas Jordan]] [http://www.rugreview.com/cw/cwcc.htm cites] {{webarchive |url=https://web.archive.org/web/20090829111849/http://www.rugreview.com/cw/cwcc.htm |date=August 29, 2009 }} 18,052 Confederate men and 37 guns engaged.</ref> McDowell's plan was to move westward in three columns and make a diversionary attack on the Confederate line at [[Bull Run Creek (Virginia)|Bull Run]] with two columns, while the third column moved around the Confederates' right flank to the south, cutting the railroad to [[Richmond, Virginia|Richmond]] and threatening the rear of the Confederate army. He assumed that the Confederates would be forced to abandon Manassas Junction and fall back to the [[Rappahannock River]], the next defensible line in Virginia, which would relieve some of the pressure on the U.S. capital.<ref>Davis, pp. 110–111.</ref> McDowell had hoped to have his army at Centreville by 17 July, but the troops, unaccustomed to marching, moved in starts and stops. Along the route soldiers often broke ranks to wander off to pick apples or blackberries or to get water, regardless of the orders of their officers to remain in ranks.<ref>Ballard, p. 8.</ref>

The [[Confederate Army of the Potomac]] (21,883 effectives)<ref name=Livermore>Livermore, p. 77.</ref> under Beauregard was encamped near Manassas Junction where he prepared a defensive position along the south bank of the Bull Run river with his left guarding a stone bridge, approximately 25 miles (40&nbsp;km) from the United States capital.<ref>{{cite web |url=https://history.army.mil/html/books/035/35-2-1/cmhPub_35-2-1.pdf |title=Battle of First Bull Run : Staff Ride Guide |author=Ted Ballard |website=History.army.mil |access-date=March 1, 2022 |archive-date=March 24, 2022 |archive-url=https://web.archive.org/web/20220324055443/https://history.army.mil/html/books/035/35-2-1/cmhPub_35-2-1.pdf |url-status=dead }}</ref> McDowell planned to attack this numerically inferior enemy army. Union [[Major general (United States)|Maj. Gen.]] [[Robert Patterson]]'s 18,000 men engaged Johnston's force (the [[Confederate Army of the Shenandoah|Army of the Shenandoah]] at 8,884 effectives, augmented by Maj. Gen. [[Theophilus H. Holmes]]'s [[brigade]] of 1,465<ref name=Livermore />) in the [[Shenandoah Valley]], preventing them from reinforcing Beauregard.
[[File:Battle of Bull Run.jpg|thumb|upright=1.35|Movements July 16–21, 1861]]
[[File:First Bull Run (Manassas) July 18.png|thumb|upright=1.35|Situation July 18]]
[[File:ATLAS OR BATTLEFIELD MANASSAS.jpg|thumb|upright=1.35|Battlefield of Manassas]]

After two days of marching slowly in the sweltering heat, the Union army was allowed to rest in [[Centreville, Virginia|Centreville]]. McDowell reduced the size of his army to approximately 31,000 by dispatching Brig. Gen. [[Theodore Runyon]] with 5,000 troops to protect the army's rear. In the meantime, McDowell searched for a way to [[flanking maneuver|outflank]] Beauregard, who had drawn up his lines along Bull Run. On July 18, the Union commander sent a [[division (military)|division]] under Brig. Gen. [[Daniel Tyler]] to pass on the Confederate right (southeast) flank. Tyler was drawn into a [[Battle of Blackburn's Ford|skirmish at Blackburn's Ford]] over Bull Run and made no headway. Also on the morning of 18 July Johnston had received a telegram suggesting he go to Beauregard's assistance if possible. Johnston marched out of Winchester about noon, while Stuart's cavalry screened the movement from Patterson. Patterson was completely deceived. One hour after Johnston's departure Patterson telegraphed Washington, "I have succeeded, in accordance with the wishes of the General-in-Chief, in keeping General Johnston's force at Winchester."<ref>Ballard, p. 9.</ref>

For the maneuver to be successful McDowell felt he needed to act quickly. He had already begun to hear rumors that Johnston had slipped out of the valley and was headed for Manassas Junction. If the rumors were true, McDowell might soon be facing 34,000 Confederates instead
of 22,000. Another reason for quick action was McDowell's concern that the ninety-day enlistments of many of his regiments were about to expire. "In a few days I will lose many thousands of the best of this force", he wrote Washington on the eve of battle. In fact, the next morning two units of McDowell's command, their enlistments expiring that day, would turn
a deaf ear to McDowell's appeal to stay a few days longer. Instead, to the sounds of battle, they would march back to Washington to be mustered out of service.<ref>Ballard, p. 10.</ref>

Becoming more frustrated, McDowell resolved to attack the Confederate left (northwest) flank instead. He planned to attack with Brig. Gen. [[Daniel Tyler]]'s division at the [[Stone Bridge (Manassas)|Stone Bridge]] on the [[U.S. Route 29|Warrenton Turnpike]] and send the divisions of Brig. Gens. [[David Hunter]] and [[Samuel P. Heintzelman]] over Sudley Springs Ford. From here, these divisions could outflank the Confederate line and march into the Confederate rear. The brigade of [[Colonel (United States)|Col.]] [[Israel B. Richardson]] (Tyler's Division) would harass the enemy at Blackburn's Ford, preventing them from thwarting the main attack. Patterson would tie down Johnston in the Shenandoah Valley so that reinforcements could not reach the area. Although McDowell had arrived at a theoretically sound plan, it had a number of flaws: it was one that required synchronized execution of troop movements and attacks, skills that had not been developed in the nascent army; it relied on actions by Patterson that he had already failed to take; finally, McDowell had delayed long enough that Johnston's Valley force, which had trained under [[Stonewall Jackson]], was able to board trains at [[Delaplane, Virginia|Piedmont Station]] and rush to Manassas Junction to reinforce Beauregard's men.<ref>Eicher, pp. 91–100.</ref>