Southern Pacific Railroad
class of steam locomotives
was the first class to be ordered by and built for Southern Pacific (SP) as cab forward
locomotives. They were built in 1909 following the design of SP's MC-1
class built earlier that year. The success of this locomotive model led to the design and introduction of the AC class of 4-8-8-2
cab forward locomotives in the 1930s and 1940s.
In order to get the fuel oil from the tender to the opposite end of the locomotive where the firebox
sat, SP had to pressurize the oil in the tender. Five pounds-force per square inch
) of air pressure was sufficient to get the oil to the fire.
The two MC-1 locomotives built in May 1909 were rebuilt in 1923 as MC-2 class with uniform cylinders measuring 22 in
diameter × 30 in stroke; these rebuilt locomotives weighed 437,000 lb, like the as-built MC-2 class, but with 393,700 lb on the drivers. Most of the rest of the MC-2 class were "simpled"<!-- technical term, should NOT be changed to "simplified" --> to the same size cylinders by 1931. Except for numbers 4011 and 4013 which were both scrapped by 1936, all of the MC-2 and the two former MC-1 locomotives were rebuilt again into class AC-1
with a higher boiler pressure, but a lower overall tractive effort
. The MC-2 rebuilds included installation of a new 4¼-BL Worthington feedwater heater
SP used these locomotives until after World War......