Southern Pacific class AC-12

Southern Pacific class AC-12
Type and origin
Power type Steam
Builder Baldwin Locomotive Works
Serial number 70082–70101
Build date October 1943 – March 1944
Total produced 20
Specifications
Configuration 4-8-8-2 Articulated
Gauge 4 ft 8 1⁄2 in (1,435 mm)
Driver diameter 63 in (1,600 mm)
Weight on drivers 531,700 lb (241.2 tonnes)
Locomotive weight 657,900 lb (298.4 tonnes)
Locomotive and tender
combined weight		 977,900 lb (443.6 tonnes)
Boiler pressure 250 psi (1.72 MPa)
Feedwater heater 6SA Worthington
Cylinders Four (simple articulated)
Cylinder size 24 in × 32 in (610 mm × 810 mm) (bore × stroke)
Performance figures
Tractive effort 124,300 lbf (553 kN)
Career
Operator(s) Southern Pacific Railroad
Class AC-12
Number(s) 4275–4294
First run October 27, 1943
Retired 1955–1958
Disposition One preserved (#4294); remainder scrapped

Southern Pacific Railroad's AC-12 class of cab forward steam locomotives was the last class of steam locomotives ordered by Southern Pacific. They were built by Baldwin Locomotive Works during World War II, with the first, number 4275, entering service on October 27, 1943, and the last, 4294, on March 19, 1944. The locomotives were effectively a conventional 2-8-8-4 locomotive running in reverse; the tender being coupled at the smokebox end of the locomotive. This was made possible by the use of oil-firing. The distinct features of these locomotives include: A steamlined front with white band, an air horn on the front, a steamlined cowcatcher, a SP 12 wheel box tender, & the air compressors are on the smokebox. Southern Pacific used these locomotives all over its system, but they were extremely famous for working on Donner Pass & Cascade Summit.

SP used the AC-12s for a little over a decade with the first retirements occurring on April 5, 1955, and the last on September 24, 1958. All but one of this class, number 4294, was scrapped.

References