July 21, 1862 Units: 2nd Maine, 2nd New Hampshire, 2nd Vermont, 1st - 4th - 5th Mass., 1st - 2nd Rhode Island, 1st - 2nd - 3rd Conn., 8th - 11th - 12th - 13th - 16th - 18th - 27th - 29th - 31st - 32nd - 35th - 38th - 39th New York, 2nd - 8th - 14th - 69th - 71st - 79th New York Militia, 27th Pa., 1st - 2nd - 3rd Michigan, 1st - 2nd Minn., 2nd Wisc., 1st - 2nd Ohio, 2nd - 3rd - 8th U.S. Regulars, Battalion of Marines, Batteries D,E,G,M, 2nd U.S. Artillery, Battery E, 3rd Artillery, Battery D, 5th Artillery, 1st - 2nd Dragoons. Losses: Union - 481 killed, 1,011 wounded, 1,460 missing or captured. Confederacy - Brig. Gen. Barnard Bee killed.

Public demand pushed General in Chief Winfield Scott to advance on the South before his troops were adequately trained. Scott had ordered General Irvin McDowell to advance on Confederate troops stationed at Manassas, Va. On July 21st, General McDowell attacked, and was initially successful, until the introduction of Confederate reinforcements resulted in a Southern victory and a chaotic retreat for the Union army towards Washington.