 Cornwallis accordingly began moving his army toward Portsmouth . This necessitated crossing the wide James River at Jamestown , a move the earl realized would give Lafayette an opportunity to attack . He decided to lay a trap for the marquis , who had come to the same conclusion when he noticed Cornwallis heading for the ferry . Lafayette 's advance force , led by General Wayne , walked into the trap , and only just escaped it , suffering 150 casualties . 
