Southern Pacific Railroad's AC-4 (meaning Articulated Consolidation) class of steam locomotives was the first class of 4-8-8-2 cab forward locomotives. They were intended to improve on the railroad's MC (Mallet-Consolidation) class 2-8-8-2 locomotives with a larger firebox, 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 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 Freight locomotives Cab forward steam locomotives