In May 1862, after the evacuation of Norfolk by Southern forces during the Peninsula Campaign, he aided in the construction of the defenses of Richmond on the James River around Drewry's Bluff. A short time later, he led his brigade at the Battle of Seven Pines, and the Battle of Malvern Hill. After the defense of Richmond, Mahone's brigade was assigned from Huger's division, to the division of Richard H. Anderson and fought at the subsequent battle of Second Bull Run, where Mahone was shot in the chest while leading his brigade in a charge across Chinn Ridge. Small of stature, , and weighing only , he was nicknamed "Little Billy". As one of his soldiers put it, "He was every inch a soldier, though there were not many inches of him." Otelia Mahone was working in Richmond as a nurse, when Virginia Governor John Letcher sent word that Mahone had been injured at Second Bull Run, but had only received a "flesh wound." She is said to have replied "Now I know it is serious for William has no flesh whatsoever."