The first Mikados that the Southern Railway procured were initially called class K and later renamed Ms. Between 1911 and 1914, a total of 135 units were delivered directly to the Southern by Baldwin and ALCO-Richmond. Together with the subsidiaries, the total number reached over 180, even if some locomotives there had differences.
The fireboxes of the locomotives were prepared directly by the manufacturers to accommodate arch tubes, but these were only installed later. Some were equipped with tractor tenders specifically for Saluda, the seven most successful of which were designated the Ms-2 class. The number 4501, which was used for special trips from 1966, is still operational today at the Tennessee Valley Railroad Museum. 