A steamship, or less commonly steam ship, is a ship that is propelled by a steam engine driving through a propeller. It usually carries the ship prefix SS before its name. Although paddle steamers are generally driven by a steam engine, they are normally counted separately and carry the prefix PS.
The term is often used interchangeably with "steamboat", although vessels called "steamboats" tend to be smaller and travel on rivers, while "steamships" are larger and travel on the open sea. The distinction is not so definite as the distinction between "boat" and "ship".
The RMS Titanic was the largest steamship in the world when it sank in 1912. Launched in 1938, the RMS Queen Elizabeth was the largest passenger steamship ever built. Launched in 1969, the RMS Queen Elizabeth 2 (QE2) was the last passenger steamship to cross the Atlantic Ocean before it was converted to diesel engines in 1986.
The SS Explorer is the last remaining steamship in Britain. She was built in Aberdeen, including the last steam engine built there, and was launched in 1955 as a fishery research vessel. Currently she is berthed at Edinburgh Dock, Leith, Edinburgh and the subject of a restoration project.