Fitz-John Porter Court-Martial: 1862-63

Porter's court-martial followed the defeat of Union forces by Confederate troops at the Battle of Second Manassas (Bull Run) in August 1862. Porter had been given command of a provisional corps created by McClellan when the latter was general in chief of all armies, a position from which he was removed by President Lincoln in March 1862 because the president believed that McClellan was not moving rapidly enough against Confederate troops. Fitz-John Porter's command was ordered to northern Virginia to reinforce the troops of General John Pope.

On August 29 General Pope transmitted orders to General Porter stressing the importance of driving the enemy from Manassas, and in successive orders instructed Porter to begin a march at 1 A.M. in order to make contact with the Confederate forces after daylight. Pope's order stated that Porter's line of march would bring him upon the right flank of Stonewall Jackson's troops and that he was to attack their rear and flank. However, Pope's understanding of the military situation was inaccurate: he did not know that on August 29, 10,000 Confederate troops under General James Longstreet had linked up with the rear of Jackson's forces, making it impossible for Porter to attack the flank and rear of Jackson's troops. Instead, Longstreet launched an attack on the Federal flank, Porter was forced to retreat, and General Pope's forces were defeated.