The railroads of the United States were nationalized during World War I, from December, 1917 to March, 1920. As part of this, locomotives built during the period were one of the twelve USRA standard designs, which included the Light Mikado. 4003 was one of 625 built by the USRA; another 641 were built after the USRA era, making it one of the most numerous single locomotive designs of all time. After Frisco received the Mikados, it modified them with boosters on the trailing trucks and raised cab roofs for more headroom.
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. Two major sources of carloads were berries, a million quarts shipped in 1941, and zinc, which was smelted in Fort Smith.
Like all the other US railroads, the Frisco actively began converting to diesel power in the late forties. 4003 was retired in early 1952, shortly before the last steam powered train on the Frisco, between Birmingham and Bessemer, Alabama in February. Frisco kept the locomotive until 1954 when it donated it to the City of Fort Smith. The city placed it on display in Kay Rodgers Park where it remained for almost 50 years. Early in this century, the city transferred the locomotive to the Fort Smith Trolley Museum with the provision that the museum pay for the moving. It now sits outside at the museum. While it could probably be restored to operating condition, the museum has no track on which to run it and the restoration cost would be considerable.