Milwaukee Road class F7
The F7s are major contenders for the fastest steam locomotives ever built, as they ran at over daily. One run in January 1941 recorded by a reporter for "Trains" magazine saw achieved twice—in the midst of a heavy snowstorm. Baron Gérard Vuillet, a French railroading expert, once recorded a run between Chicago and Milwaukee where the locomotive reached and sustained an average for . However, the British locomotive LNER Class A4 4468 "Mallard" is officially accepted to be the world's fastest, with a run recorded at but authenticated at 126 mph in 1938.
James Holden (locomotive engineer)
The Decapod developed mainly under Chief Draughtsman Frederick Vernon Russell was an extraordinary endeavour to develop a steam locomotive which could perform at the level of electric traction. It was built in 1902 to forestall an imminent scheme for an electrified railway out of London to suburbs served by the GER. Since the proponents of the scheme had a slogan about electric trains accelerating to thirty miles an hour in thirty seconds, Holden resolved to obtain the same performance with steam traction. A massive boiler with Wootten firebox, three cylinders each with its own blastpipe cone, and ten smallish driving wheels ensured a lively acceleration. On trial it did rather better than 30 mi/h (50 km/h) in thirty seconds, accelerating at 1.46 ft/s² (0.45 m/s²): This performance put an end to the electrification scheme even though (as Holden had known all the time) the regular use of so massive a machine would never have been permitted by the civil engineer.