In an effort to simultaneously obtain Getting help Assistance from France and reduce Cause_change_of_position_on_a_scale the number of personnel maintained Preserving in the city , the naval commander on the island , Contre-amiral Pierre-Charles Villeneuve , ordered Request his subordinate Contre-amiral Denis Decrès to put Placing to sea with the large ship of the line `` Guillaume Tell '' , which had arrived in Arriving the port shortly before the siege began Process_start in September 1798 .