Alan, as Bob said, the ACS was a staff position which had no combat duties. I've read only one account written by an ACS -- with a dismounted Texas cavalry regiment, if I recall correctly. During a battle or when on the march, he was with the supply train, well to the rear of the army. He spent a lot of his time obtaining commissary supplies, either through requisition or by sending out foragers, assisted by a commissary sergeant and several teamsters detailed from the line regiments.