Southern Pacific Railroad owned and operated eleven classes of cab forward steam locomotives. Their AC-12 class of simple articulated 4-8-8-2 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, SP 4294, on March 19, 1944. Each locomotive was effectively a conventional 2-8-8-4 locomotive running in reverse, the tender being coupled at the smokebox end of the locomotive. The design was able to deal with the peculiar problems of its routes, particularly the 39 long tunnels and nearly 40 miles (64 km) of snow sheds of the Railroad's crossing of the Sierra Nevada via Donner Pass could funnel dangerous exhaust fumes back into the crew compartment of a conventional locomotive. Fuel and water were pressurized to allow a steady flow, even on steep mountain grades. Visibility from the cab was superb, as one crewman could easily survey both sides of the track. The distinct features of these locomotives include: a streamlined front with white band, an air horn on the front (along with a steam whistle on the boiler), a streamlined pilot, an 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.
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. Only one cab forward, AC-12 4294, has survived into preservation and is now on display at the California State Railroad Museum.
I was fortunate enough to catch this massive locomotive, so distinctive to the Southern Pacific, in 1978, before it was "entombed" in the CSRM. Click on the "Locomotive Number" here on RailPictures, then go to the first page of photos of this monster, to see it outdoors. (Sacramento, California – June 23, 2025)
