Brockenbrough assumed command of the brigade after Field was wounded at the Second Battle of Bull Run and led it two days later at Chantilly. During the Maryland Campaign, Brockenbrough took part in the capture of Harpers Ferry, and then marched with the rest of the Light Division to the rescue of Gen. Robert E. Lee's army at Sharpsburg; his brigade was deployed on the far right of A.P. Hill's line and did not see any direct action there. At Fredericksburg, his brigade was ordered to plug a hole in the Confederate line that was being exploited by Union troops under Maj. Gen. George G. Meade. Brockenbrough lost control of his brigade during this action and two of his regiments split off with him and never reached the fighting. Lee apparently was not impressed with Brockenbrough's leadership qualities. Even though months had passed, the unit was still called Field's Brigade and Brockenbrough was still considered its temporary commander. Lee did not recommend John for promotion.