Southern Pacific Railroad's AC-2 class of steam locomotives was the second in the AC series of cab forward locomotives built for Southern Pacific (SP). This class consisted of locomotives that were rebuilt from Baldwin-built SP MC-4 class locomotives by 1930. The rebuild from MC-4 class gained the locomotives about 5,000 pounds-force (22 kN) in tractive effort, but also increased the locomotives' weight by about 50,000 pounds (23,000 kg). The locomotives were deemed successful and remained in active service until after World War II.