As steel cars became more numerous on Southern Railroad passenger trains between Washington, DC and Atlanta, GA, the 4-6-2 "Pacifics" were unable to maintain running times. In need of more power the Southern bought 23 "Mountains" (road numbers 1450 through 1472) from the Baldwin Locomotive Works in 1917.

These locomotives were designated Class Ts and weighed 314,800 lbs and had 27 x 28 cylinders, 69" drivers, a boiler pressure of 200 psi and exerted 50,300 lbs of tractive effort.

In 1919, Baldwin delivered 25 USRA "Mountains" (road numbers 1475 through 1499). They were designated Class Ts-1 and weighed 327,000 pounds. They had 27 x 30 cylinders, 69" drivers, a 200 psi boiler pressure and exerted 53,900 lbs of tractive effort.

The Southern "Mountains" ran on the Washington to Atlanta main line working in both directions out of Spencer, NC.

There were ten other "Mountains" built by Baldwin for two of the Southern Railroad subsidiaries. Five of the Class Ts locomotives (road numbers 6490 through 6494) were built for the Cincinnati, New Orleans & Texas Pacific in 1917. Five were built for the Alabama Great Southern. These were two Class Ts (road numbers 6695 and 6696) built in 1917 and three Class Ts-1 (road numbers 6692 through 6694) built in 1919.

Neither the Southern Railroad nor its subsidiaries saved any of the "Mountains" for posterity.