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.
New York Central Niagara
The American Locomotive Company ALCO proposed these locomotives, and although the design owes something to the Union Pacific 4-8-4's, of which Union Pacific 844 is the best-known, the design was actually quite new. Some steam experts have claimed the Niagara to be the ultimate locomotive, as it had the speed of an FEF (the Union Pacific's nickname for their 'four eight fours' was FEF) and the power of Northerns with smaller driver wheels.