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.
4-6-4
The Chicago, Milwaukee, St. Paul and Pacific Railroad (Milwaukee Road) could have produced the first American since its design work was done earlier than that of the NYC, but financial constraints delayed the project and the Milwaukee's locomotives only emerged in 1930. The Milwaukee called them Baltic, following the European practice started in France. The initial order of fourteen Class F6 locomotives was followed by eight more Class F6a locomotives in 1931 and, in 1938, the Milwaukee acquired six streamlined Class F7 Hudsons with the shrouds. These took over the Milwaukee's crack "Hiawatha" express trains from the Class A Atlantics and were among the fastest steam locomotives of all time. The schedules of many of these trains required extended running at .