The first locomotives that Southern Pacific had built as cab forwards were the MC-2. They were similar to the MC-1, but were reversed with the cab at the front. In order to be able to transport the oil into the firebox, the tender had an overpressure of five psi. The exhaust steam from the high-pressure cylinders was reheated before being passed into the low-pressure cylinders. In 1909 a total of 15 of this class were built and the two MC-1 were rebuilt into the MC-2.

A further twelve MC-4 followed in 1911, which were virtually identical to the MC-2. In contrast, the 20 MC-6 that were delivered in 1912 and 1913 already had a superheater. To increase the speed of the locomotives, they were rebuilt between 1930 and 1937 with four identical cylinders, a larger superheater and a Worthington feedwater heater. The MC-2, MC-4 and MC-6 became the AC-1, AC-2 and AC-3, which now stood for “Articulated Consolidation”. They were used in the Second World War for freight trains, but also for passenger trains and troop transports, and were retired between 1946 and 1949.