They were assigned to haul and bank heavy freight trains over the Saluda Grade and Old Fort Loops in the Blue Ridge Mountains of North Carolina.

Ever since the Santa Fe Railway develop the 2-10-2 wheel arrangement (hence the Railroad's namesake) in 1903, the Southern Railway (SOU) began placing a new order of their own 2-10-2s; the Ss class were built with 57 in (1,448 mm) driving wheels, duplex stokers, 71,000 lb (32.2 tonnes) of tractive effort, and an operating boiler pressure of 190 psi (1.31 MPa).

[1] These locomotives were designed to haul heavy freight trains, but were proven too slow to work on the Southern Railway's Washington, D.C. to Atlanta main line and too big for the CNO&TP tunnels' tight clearances.

[1][3] However, the Ss locomotives were very efficient on handling the mountain grades in North and South Carolina, Georgia, and Tennessee.

[2] While they were used to bank the head end passenger trains, the Ss locomotives were given cab signals and steam brake connection; and the water pipes were added to cool down the driving wheels' tires while descending the mountains.