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.
Milwaukee Road class F7
The Milwaukee F7s are accepted as the fastest steam locomotives by a different measure—scheduled speed between stations. In 1939, shortly after they were introduced into passenger service, the "Twin Cities Hiawatha" schedule was modified such that the engines would need to run the between Portage and Sparta, Wisconsin in 58 minutes—a start-to-stop average of .