During the Battle of Antietam, as lieutenant colonel of his regiment, he was wounded again in the right leg as his regiment was decimated along with the rest of Maj. Gen. John Sedgwick's division during an ambush.
Under Slaget ved Antietam, som oberstløjtnant for sit regiment, blev han såret igen i højre ben, mens hans regiment blev decimeret sammen med resten af Generalmajor John Sedgwick's division i et baghold.