Ever since the
Santa Fe Railway develop the 2-10-2 wheel arrangement (hence the Railroad's namesake) in 1904, the Southern Railway (SOU) began placing a new order of their own 2-10-2s; the Ss class were built with the first batches of fifty-five locomotives (Nos. 5000-5054) in 1917 by the Baldwin Locomotive Works in
Philadelphia, Pennsylvania. These locomotives were equipped with driving wheels,
duplex stokers, four
sand domes, Southern valve gear, and cylinders with an operating boiler pressure of , which made them produced of tractive effort. They were also equipped with a two-axle bogie tender with a fuel capacity of of coal and of water. In 1918, the second batches of twenty-five 2-10-2s (Nos. 6350-6374) were built by the American Locomotive Company (ALCO) of
Richmond, Virginia for SOU's
Cincinnati, New Orleans and Texas Pacific (CNO&TP) division. The CNO&TP locomotives were equipped with a wimble
smoke duct due to the CNO&TP route traveling through 27
tunnels between
Danville, Kentucky and
Harriman, Tennessee, earning the nickname
The Rathole Division. The Ss class were designed to haul heavy freight trains, but were proven too slow to work on the Southern Railway's
Washington, D.C. to Atlanta mainline and too big for the CNO&TP tunnels' tight clearances. Thus, No. 6350-6374 were renumbered to 5055-5079. Eventually, they were moved to Southern's
Asheville and
Knoxville divisions to bank and haul heavy freight trains, especially on Saluda Grade between Asheville, North Carolina and
Spartanburg, South Carolina and the Old Fort Loops between Asheville and
Salisbury, North Carolina in the Blue Ridge Mountains. To work on the Asheville Division, the Ss locomotives were modified with two
water gauges made longer for the
engineer and
fireman to safely measure the water level in the boiler while going up and down the railway grades. Additionally, the Ss locomotives were equipped with a second
air pump due to the excessive use of
air brakes. 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. By the late 1940s, the Southern Railway began to
dieselize with the Ss steam locomotives' duties taken over by the
EMD F7 diesel locomotives. All of the Ss steam locomotives were retired and scrapped by the early 1950s, with none surviving into preservation. ==See also==