Mainline steam trains in Great Britain
The most famous steam locomotive operating on the British main line is the 1923 built "Flying Scotsman". After being taken into public ownership in 2004, following a decade long refit it returned to mainline service in 2016. The fastest steam locomotive ever built, the 1938 built "Mallard", was also certified for main line operation briefly in the 1980s.
Chessie (train)
To pull the "Chessie" the C&O ordered three experimental steam turbine locomotives from the Baldwin Locomotive Works. As diesel locomotives became more prevalent following World War II, the C&O was one of several railroads loath to abandon coal as a fuel source, and saw steam turbine technology as a possible alternative to diesel. At the time of their construction these locomotives were the longest single-unit locomotives in the world. Not including research and development, the three locomotives cost . The M1s proved a failure in operation and were scrapped in 1950.