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SP AC-12 Cab Forward Locomotive No. 4289.
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SP AC-12 Cab Forward Locomotive No. 4289.

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Southern Pacific Class AC-12 Cab Forward Locomotive
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.

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.

Southern Pacific Class AC-12 Overview
Type and origin
Power: type Steam
Builder: Baldwin Locomotive Works
Serial numbers: 70082–70101
Build dates: October 1943 – March 1944
Total produced: 20
Configuration: 4-8-8-2 Articulated
Gauge: 4 ft 8 1⁄2 in (1,435 mm) standard gauge
Driver diameter: 63 in (1,600 mm)
Adhesive weight: 531,700 lb (241,200 kg; 241.2 t)
Loco weight: 657,900 lb (298,400 kg; 298.4 t)
Total weight: 977,900 lb (443,600 kg; 443.6 t)
Boiler pressure: 250 psi (1.72 MPa)
Feedwater heater: 6SA Worthington
Cylinders: Four (simple articulated)
Cylinder size: 24 in × 32 in (610 mm × 813 mm) (bore × stroke)
Performance figures
Tractive effort: 124,300 lbf (553 kN)
Operator: Southern Pacific Railroad
Class: AC-12
Numbers: 4275–4294
First run: October 27, 1943
Retired: 1955–1958
Disposition: One preserved (No. 4294); remainder scrapped

See also:

Cab Forward Locomotives

Southern Pacific