The United States Railroad Administration reassigned 23 of them (road numbers 4000-4007 and 4017-4031) to the St. Louis–San Francisco Railway (SLSF), also known as the "Frisco".

As part of this, locomotives built during the period were one of the twelve USRA standard designs, which included the Light Mikado.

After Frisco received the Mikados, it modified them with boosters on the trailing trucks and raised cab roofs for more headroom.

[3] The Frisco put it into service hauling freight between Fort Smith, Arkansas and Monett, Missouri, which included a stretch through the Boston Mountains that was relatively steep.

4003 was retired in early 1952, shortly before the last steam powered train on the Frisco, between Birmingham and Bessemer, Alabama in February.