At that date, July 4, 1861, the rebels had two armies in front of
Washington; the one at Manassas Junction, commanded by General
Beauregard, with his advance guard at Fairfax Court House, and
indeed almost in sight of Washington. The other, commanded by
General Joe Johnston, was at Winchester, with its advance at
Martinsburg and Harper's Ferry; but the advance had fallen back
before Patterson, who then occupied Martinsburg and the line of the
Baltimore & Ohio Railroad.

The temper of Congress and the people would not permit the slow and
methodical preparation desired by General Scott; and the cry of "On
to Richmond!" which was shared by the volunteers, most of whom had
only engaged for ninety days, forced General Scott to hasten his
preparations, and to order a general advance about the middle of
July. McDowell was to move from the defenses of Washington, and
Patterson from Martinsburg. In the organization of McDowell's army
into divisions and brigades, Colonel David Hunter was assigned to
command the Second Division, and I was ordered to take command of
his former brigade, which was composed of five regiments in
position in and about Fort Corcoran, and on the ground opposite
Georgetown. I assumed command on the 30th of June, and proceeded
at once to prepare it for the general advance. My command
constituted the Third Brigade of the First Division, which division
was commanded by Brigadier-General Daniel Tyler, a graduate of West
Point, but who had seen little or no actual service. I applied to
General McDowell for home staff-officers, and he gave me, as
adjutant-general, Lieutenant Piper, of the Third Artillery, and, as
aide-de-camp, Lieutenant McQuesten, a fine young cavalry-officer,
fresh from West Point.