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.
GNRI Class Q
Faster running was achieved with the addition of superheated boilers and widened cylinders (under the supervision of G.T. Glover in the 1920s). In 1932 a two coach newspaper train hauled by No. 135 covered Howth Junction to Drogheda at a start-to-stop average speed of , the fastest run in Ireland achieved with a steam locomotive on a scheduled train