Early on the 20th, Porter pushed the V Corps brigades of Gens. James Barnes, Charles Lovell and Gouverneur Warren across the Potomac to establish a bridgehead. Hill’s division counterattacked while many of the Federals were crossing and nearly annihilated the 118th Pennsylvania (the “Corn Exchange” Regiment), inflicting 269 casualties of 737 men. Porter withdrew back across the river. The two-day fight at Shepherdstown discouraged McClellan from pursuing Lee’s retreating army.