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.
4-4-2 (locomotive)
The locomotives were cross balanced and ran on drivers. They had an oil-fired grate and a rated boiler pressure of , which gave the boiler a high capacity in relation to the cylinders. Designed for a light-weight train of five to six passenger cars, they were considered as probably the fastest steam locomotives ever built in the United States, possibly capable of matching any locomotive in the world. The fleet covered their schedule in 400 minutes with several stops en route, at an average speed of more than on some sections and often arriving with one or two minutes to spare.