Southern Pacific Railroad The Southern Pacific (or Espee from the railroad initials- SP) was an American Class I railroad network that existed from 1865 to 1996 and operated largely in the Western United States. The system was operated by various companies under the ...

's AC-4 (meaning Articulated Consolidation) class of

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

s was the first class of

4-8-8-2 Under the Whyte notation for the classification of steam locomotives, a 4-8-8-2 is a locomotive with four leading wheels, two sets of eight driving wheels, and a two-wheel trailing truck. Other equivalent classifications are: UIC classification ...

cab forward The term cab forward refers to various rail and road vehicle designs that place the driver's compartment substantially farther towards the front than is common practice. Rail locomotives In steam locomotive design, a cab forward design will ...

locomotives. They were intended to improve on the railroad's MC (Mallet-Consolidation) class

2-8-8-2 A 2-8-8-2, in the Whyte notation for describing steam locomotive wheel arrangements, is an articulated locomotive with a two-wheel leading truck, two sets of eight driving wheels, and a two-wheel trailing truck. The equivalent UIC classification ...

locomotives with a larger

firebox Firebox may refer to: *Firebox (steam engine), the area where the fuel is burned in a steam engine *Firebox (architecture), the part of a fireplace where fuel is combusted *Firebox Records, a Finnish 8101705801record label * Firebox.com, an electro ...

, hence, the four-wheel leading truck (instead of the two-wheel). The AC-4s were the first SP Mallets built for simple expansion.

Baldwin Locomotive Works The Baldwin Locomotive Works (BLW) was an American manufacturer of railroad locomotives from 1825 to 1951. Originally located in Philadelphia, it moved to nearby Eddystone, Pennsylvania, in the early 20th century. The company was for decades t ...

built them in August through October 1928 with a maximum cutoff of 70%, so tractive effort was rated at ; a few years later, limited cutoff was dropped and calculated tractive effort increased to . The AC-4s were removed from service starting in 1953, and all ten were scrapped by June 1955.

References

* AC-04 4-8-8-2 locomotives Baldwin locomotives Simple articulated locomotives Railway locomotives introduced in 1928 Steam locomotives of the United States Scrapped locomotives Standard gauge locomotives of the United States {{steam-loco-stub Freight locomotives Cab forward steam locomotives