Southern Pacific Railroad's AC-6 class of steam locomotives was the third of the railroad's classes built with a 4-8-8-2 wheel arrangement. Like the earlier AC-4 and AC-5 classes, the AC-6 class were cab forward locomotives. The AC-6 was slightly larger than the previous classes with a higher boiler pressure and tractive effort rating. This class was removed from active service between 1954 and 1955 and they were all scrapped by March 1956.