Is it ensure, insure, or assure?
1794, shortened from line-of-battle ship (1705), one large enough to take part in a main attack (formerly one of 74-plus guns); from battle (n.) + ship (n.). Later in U.S. Navy in reference to a class of ships that carried guns of the largest size. The last was decommissioned in 2006. Battleship-gray as a color is attested from 1916. Fighter and bomber airplanes in World War I newspaper articles were sometimes called battleplanes, but it did not catch on.