In order to increase average speeds in the fight against other railroads, the Milwaukee Road had ALCO build four class A streamlined locomotives from 1935 onwards. In order to save weight, not only particularly light passenger cars were developed for the “Hiawatha”. Weight was also saved on the locomotives by choosing the 4-4-2 wheel arrangement, which was no longer used in the USA by this time.

By only having two driving axles, the moving masses could be reduced. Furthermore, the first driving axle was driven, which led to shorter connecting rods. Additionally, a boiler pressure of 300 psi (20.7 bars) was used, allowing smaller cylinders with lighter pistons to be used. Despite only two cylinders and the imperfect mass balancing, high speeds could be achieved with seven-foot drivers.

Shortly after its delivery in May 1935, number two reached a speed of 112.5 mph (181 km/h), which could be counted as a world record thanks to the dynamometer car that was present. There are also unconfirmed reports of speeds in excess of 120 mph. What is undisputed, however, is that they were able to travel at sustained speeds in excess of 100 mph with their light trains.

The 422 miles from Chicago to St. Paul were to be completed in six and a half hours with eleven stops. In fact, the trains completed this route in six and a quarter hours. Even after the introduction of the more powerful class F7 Hudsons, they continued to pull the Hiawatha. Between 1949 and 1951 they were replaced by diesel locomotives.