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.
American Locomotive Company
Alco was the second-largest steam locomotive builder in the United States (after Lima Locomotive Works), producing over 75,000 locomotives (though not all were steam, since, unlike Baldwin, Alco transitioned more readily to Diesel). Among these were a large number of well-known locomotives. Railroads that favored Alco products included the Delaware & Hudson Railway, the New York, New Haven & Hartford Railroad, the New York Central Railroad, the Union Pacific Railroad and the Milwaukee Road. Alco was known for its steam locomotives of which the 4-6-4 Hudson, 4-8-2 Mohawk and the 4-8-4 Niagara built for the New York Central and the 4-8-4 FEF and the 4-6-6-4 (Challenger) built for the Union Pacific were fine examples. Alco built many of the biggest locomotives ever constructed, including Union Pacific's "Big Boy" (4-8-8-4). Alco also built the fastest American locomotives, the Class A Atlantic and Class F7 Hudson streamliners for the Milwaukee Road's "Twin Cities Hiawatha" run. Among the ambitious state-of-the-art designs of the late steam era, Alco's Challengers, Big Boys and high speed streamliners stood out for their in-service success.