Southern Pacific’s Cab Forward

Southern Pacific’s signature, and most iconic locomotive was the 256 AC (Numbers 4000 to 4294) cab forward locomotives.

These were some of the largest and most unique locomotives in the United States. The AC-12 class is less than ten feet shorter than the largest steam locomotives ever built: Union Pacific’s “Big Boy”. The AC-12 locomotive and tender weighed more than a Boeing 747 and an Airbus A380, combined.

The reason the cab forwards were unique is that, as the name implies, the crew cab was in the front of the locomotive, like a modern diesel-electric locomotive, instead of the cab being in back, near the tender.

Having the cab in front gave the engineer and fireman unequalled views of the track ahead. But the real reason for the innovations was to conquers the steep grades of Sacramento’s Mountain Subdivision over the Donner Pass. This massive locomotives operated between Roseville, Ca and Sparks, Nv where a powerful locomotive was needed to tackle the steep grades and have the tractive effort to haul long freight trains over the Sierra Nevada Mountains. A locomotive of this size emits of lots of steam exhaust because a 4-8-8-2 was essentially two locomotives in one.

The Donner Pass route had 40 miles of snow sheds and 39 tunnels. This meant that in a standard locomotive, the crew could suffer from asphyxiation from the steam exhaust. By putting the cab forward, the exhaust stack was behind the crew and they avoided the caustic smoke, steam, and heat that these powerful locomotives emitted.

The cab forward proved to be a very successful locomotive for SP, with 256 of these engines used on it’s rail over the period of 50 years. The railroad had the largest fleet of articulated “Malleys” in the world. As a comparison, Union Pacific fleet contained 25 Big Boy locomotives.

In the 1950s, as diesel replaced steam, cab forwards spend the rest of there working life away from the mountains on the Coast Line and the Western Division. One of the last places cab forwards worked on Southern Pacific rail was the Cal-P line between Oakland and Roseville. 1958 was the last year a cab forward rode the rails, nine of these locomotives were taken out of service on September 24, 1958.

Out of the 256 cab forwards that were built, only one survives. The AC-12 number 4294 which is also the last steam locomotive that Southern Pacific ever purchased. 4294 was in service on March 19, 1944 and was taken off the the roster on March 5, 1956. She was only in service for 12 years.

While the other cab forwards were scrapped, 4294 was put in storage and then was put on static display on October 19, 1958, in front of the Sacramento train station. When the California State Rail Road Museum was opened, 4294 became the centerpiece amongst it’s collection of locomotives and rolling stock.

I was at the museum with my father in 1981 for the official opening of the museum. SouthernPacific’s GS-4 4449 and Union Pacific’s 844 (then numbered 8444) where in attendance and I will never forget when the two locomotive stood, pilot to pilot, on the track outside of the museum!

The massive running gear of the AC-12, Cab Forward. 4294 is the only surviving example of this locomotive.

The last time I have visited the museum was in November of 2017 where I did an aborted field sketch of the cab forward. There was something about the proportions of the locomotive that I did not get right. I had planned to return to the California State Rail Museum in the early Spring of 2020 but the cases of Covid-19 were growing at an alarming rate in the state and the museum eventually closed it’s doors for an indeterminate time.

So if I could not sketch the AC-12, at least I could sketch it from an image, which really is the next best thing.

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