The first major campaign was driven by the theory that the war would be won if the opposing capital could be captured. With the growing host of Federal troops descending on Washington, it appeared that the South would, by necessity, be thrown into a defensive mode. Beauregard, however, proposed an ambitious offensive to Confederate President Jefferson Davis. His plan called for combining his army with Gen. Johnston’s near Harpers Ferry and attacking Patterson’s smaller command. With Patterson’s army defeated, the Confederates would then move east and fall upon McDowell, whose defeat would leave Washington exposed to capture. Davis rejected the idea. With Beauregard forced on the defensive, the initiative fell to McDowell as to when and where he would launch his growing army against the Confederates in northern Virginia. In order to do so, however, McDowell would need Gen. Patterson to hold Johnston’s Confederate army in the Shenandoah Valley.
Beauregard spent considerable time examining the terrain south of Centreville. His engineering background helped him quickly discern that this area, bisected by a creek called Bull Run, offered outstanding defensive positions. The deep waterway was largely impassible except at a handful of fords, behind which Beauregard could concentrate his men. By the end of June, Beauregard had three of his five brigades aligned behind Bull Run. The other two brigades, Bonham’s at Fairfax Court House and Ewell’s at Fairfax Station, occupied advanced positions on the east side of the creek.1
Skirmishes between the two opposing armies grew in frequency with each passing week. In an effort to test Confederate strength and repair and guard the railroad, McDowell on June 17 sent about 700 men from the 1st Ohio (Schenck’s brigade) toward Vienna on the Loudoun & Hampshire Railroad. Elements from Bonham’s Brigade quickly put an end to the excursion.2
Once he left Pennsylvania, Patterson intended to sweep through Maryland during the first week of June, cross the Potomac River at Williamsport, and capture Harpers Ferry. He did not finish organizing his army until June 11, however, and it was not until June 15 that his campaign actually began. An old officer with some experience leading men in battle in Mexico, Patterson overestimated the size of his adversary’s army and claimed that he lacked the wagons and horses to mount an expeditious advance. Patterson waved off frequent rumors that Johnston had (or was about to) evacuate Harpers Ferry. To his way of thinking, Johnston would never give up the town without a fight. The rumors, however, were true. Johnston knew he did not have enough men to defend the heights ringing the town. When he learned of Patterson’s pending advance, he moved his wagons and supplies south toward Winchester on June 13, with his men following two days later. Patterson occupied Harpers Ferry without incident on June 16.3
Gens. McDowell and Scott met with President Lincoln (the primary mover behind the operation) and his cabinet on June 29 to discuss plans for an advance against Manassas Junction. The operation would involve some 30,000 Federals, with another 10,000 held in reserve. The plan called for Tyler’s large division, on McDowell’s right flank, to march south by way of Vienna and cut between Centreville and Fairfax Court House, where it would join the middle column under Col. Hunter on the Little River Turnpike. This movement would cut off Bonham’s Brigade at Fairfax Court House. McDowell’s left column comprised of Heintzelman’s division, meanwhile, would march along the Orange and Alexandria Railroad and eventually meet the other two Federal columns somewhere north of Bull Run. The overall objective of these movements was to turn Beauregard’s right flank, and so avoid assaulting the heavily defended fords along Bull Run. The details still needed to be worked out, but the basic strategy was sound. No one raised serious doubts about the plan, but Gen. Charles Sandford was pessimistic about Patterson’s ability to hold Johnston in the Shenandoah Valley. The campaign was slated to begin on July 8, but McDowell’s army was not ready by that day. The men moved out about 2:00 p.m. on July 16.4