It was under the command of Major General Robert Patterson, its manpower mainly consisted of three-month troops from the states of Pennsylvania and New York.

"Within four days after the disaster at Bull's Run, eleven regiments of this fine body of men (armed, drilled, clothed, equipped, and in all respects ready for active service) were in Washington," Governor Andrew G. Curtin reminded the State Legislature.

[2] On July 2, 1861, Major General Robert Patterson's army, called the Department of Pennsylvania, crossed the Potomac River near Williamsport, Maryland, and marched on the main road toward Martinsburg, Virginia.

During the afternoon of July 21, 1861, the arrival of BG General Joseph E. Johnston reversed the tide of Battle, the ensuing Confederate counterattack turned victory into a rout, and euphoric Northern hopes for a short war were quickly dashed.

He sought to redress the record through every possible avenue, including a personal audience with President Abraham Lincoln, and later published his own version of events.