Titanic's Tragic Sister: Although the Titanic is arguably the most famous ship in history, the story of that vessel's sister ship, the HMHS Britannic is just as interesting. Planned as a cruiser, the ship was eventually used as a floating hospital in the First World War. On Novemer 21, 1916 the ship sank, and the reasons for that disaster have never been made entirely clear. This documentary tells the story of this remarkable boat