Southern Pacific class AC-12

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 streamlined front with white band, an air horn on the front, a streamlined pilot, a SP 12 wheel box tender, and air compressors mounted on the smokebox. Southern Pacific used these locomotives all over its system, but they were extremely famous for working on Donner Pass & Cascade Summit.

Southern Pacific class AC-12
Type and origin
Power typeSteam
BuilderBaldwin Locomotive Works
Serial number7008270101
Build dateOctober 1943 March 1944
Total produced20
  Whyte4-8-8-2 Articulated
Gauge4 ft 8 12 in (1,435 mm) standard gauge
Driver dia.63 in (1,600 mm)
Adhesive weight531,700 lb (241,200 kg; 241.2 t)
Loco weight657,900 lb (298,400 kg; 298.4 t)
Total weight977,900 lb (443,600 kg; 443.6 t)
Boiler pressure250 psi (1.72 MPa)
Feedwater heater6SA Worthington
Cylinders4 (simple articulated)
Cylinder size24 in × 32 in (610 mm × 813 mm) (bore × stroke)
Performance figures
Tractive effort124,300 lbf (553 kN)
OperatorsSouthern Pacific Railroad
First runOctober 27, 1943
DispositionOne preserved (#4294); remainder scrapped

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, were scrapped.


  • Diebert, Timothy S. & Strapac, Joseph A. (1987). Southern Pacific Company Steam Locomotive Conpendium. Shade Tree Books. ISBN 0-930742-12-5.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.