Ocean liners played a major role in World War I. Large ocean liners such as the Mauritania and Olympic were used as troopships and hospital ships while smaller ocean liners were converted to armed merchant cruisers. The Britannic, sister to the Titanic and Olympic, never served on the liner trade for which she was built, instead entering war service as a hospital ship as soon as she was completed—she lasted a year before being sunk by a mine.