In the wake of the Battle of Fort Sumter and President Abraham Lincoln's subsequent call for 75,000 volunteers in the spring of 1861, the Commonwealth of Pennsylvania began organizing regiments for ninety days' service in the Union Army.

As companies of volunteers and militiamen began arriving in the state capital at Harrisburg, the men were gathered north of the city at Camp Curtin.

The next day they were sent to Washington but their train was halted near Cockeysville, Maryland because Secessionists had burned a railroad bridge as part of the Baltimore Riot.

The 2nd Pennsylvania did not take part in the skirmish, but were in close supporting distance and arrived on the battlefield shortly after Jackson retreated.

Patterson had been entirely fooled by Johnston, who transferred the bulk of his army from the Shenandoah Valley to Manassas Junction where they played a decisive part in the Confederate victory at the Battle of Bull Run.