 A few days prior to the action on Malvern Hill , McClellan incorrectly believed that the Army of the Potomac was vastly outnumbered by its Confederate foe , and his fear of being cut off from his supply depot left him cautious and wary . On the night of June 28 , McClellan told his generals that he intended to move his army to a position on the north bank of the James River called Harrison 's Landing , where they would be protected by Union gunboats . The Army of the Potomac came to Malvern Hill , the army 's final stop before reaching the Landing , with approximately 54 @,@ 000 men . 
