For the well-known Saluda grade of more than four percent, the Southern was looking for a locomotive with a particularly high tractive effort. This is where the idea came up of accommodating additional driven axles in the tender and thus using the tender as an additional adhesive weight. There were several designs, of which only the Ms-2 made it to seven.

As with all of these experimental machines, the Ms-2 was created from a conventional steam locomotive and the frame of another, older locomotive, on which a tender body was mounted. The modern class Ms Mikado was used as the locomotive, while the frame of the tender came from an older Consolidation. The five machines assembled in this way left the Southern Railway workshops in Spencer, North Carolina in 1915. A pipe went directly from the superheater exit into the tender, supplying steam to the rear engine when needed.

While the locomotive's coupling wheels were 63 inches, the tender's coupling wheels were only 50 inches, which must have led to an unusual exhaust noise. The tender's cylinders were bushed from the original 20 to 18 inches in diameter. The cylinders of the locomotive were also bushed from 27 to 26 inches to save steam. Compared to the original Ms, 1,400 instead of the previous 1,100 tons could now be towed on a gradient of 1.7 percent.

In addition to the Ms-2, other Mikados were built with a tender with a 2-6-0 wheel arrangement or locomotives with a 2-10-2 wheel arrangement with a tender with a 2-6-0 wheel arrangement. What they all had in common was the clearly decreasing tractive effort as the tender emptied. While tank locomotives still have a significant weight even with almost empty supplies, the empty weight of the tender was very low. In addition, the exhaust from the rear engine was blown into the air above the tender, which must have reduced the draft in the boiler. Just a few years later, the Ls-1 class Mallets took over the Saluda grade.