A Union Ship is a type of ship that was used during the American Civil War. The term 'Union Ship' refers to any vessel that was owned and operated by the United States Navy during the war. The most famous of these ships was the USS MONITOR, which was a revolutionary ironclad warship that was designed to fight against Confederate vessels. The term 'MONITOR' is derived from the Latin word for 'WARNING, ' and it was given to the ship because of its role in WARNING the Union forces of potential attacks.