A steam locomotive that looks like it’s running backwards – when heading straight toward you! For nearly 50 years, the Southern Pacific (SP) Railroad hauled freight and passenger trains throughout California, over the Sierras and through the SP system using these articulated consolidation locomotives. SP used the designation AC for these locomotives. SP needed the power of these massive steam locomotives to get freight over the mountains, and the crew needed the cab in front for safety.
Some people call them “cab-in-front locomotives,” others call them “back-up locomotives.” The railroad and most railfans call them “Cab Forwards”. They were the epitome of Southern Pacific steam power, the result of years of experience and the ever-expanding need for speed, power, and improved tractive effort. More importantly, for the design of these locomotives, Cab Forwards protected train crews from the dangerous smoke exhaust that could cause asphyxiation in snow sheds and tunnels.
What is a Cab Forward?
The history of the Southern Pacific Cab Forward wouldn’t make much sense without defining what a Cab Forward actually is. So before going into the historical background of the Southern Pacific Cab Forward, let’s delve briefly into the term “Cab Forward”.
As the name implies, a “cab forward” refers to any form of a rail vehicle that puts the driver’s compartment at the front of the locomotive and in front of the boiler than is commonplace. In other words, the cab or the driver’s compartment is placed in front of the boiler and at the very front of the engine.
While this design wasn’t common in the early 20th century, it was widely used by the Southern Pacific and became some sort of a signature design for the company.
Historical Background of the Cab Forwards
In the early 20th century, the states that bordered California to the east were experiencing a surge in population. Business in California was booming and Southern Pacific had to ship more agricultural products and manufactured goods.
Trains were not only getting longer but also heavier and the company required more power to handle the increasing transportation demands. To deal with this issue, Southern Pacific commissioned two Mallet-type 2-8-8-2 articulated steam locomotives (No 4000 and No 4001) in 1908. These Mallet-type were powerful enough to handle the steep Sacramento Division, which was a 150-mile stretch over the Sierra Nevada (Sierra Nevada is Spanish for “mountain range covered in snow”) and had always been a challenge for man and machine.
While the Mallet locomotives proved to be a perfect match for the power that SP needed in handling heavier and longer trains over the Sierras, the company soon realized that the tunnels and snow sheds along the way between Sparks, Nevada, and Roseville, California made life unbearable for the crew. The trains had to go through 39 tunnels and almost 40 miles of snow sheds to be precise.
The stack gasses discharged by the locomotives from the boilers concentrated within these tunnels and snow sheds. This proved dangerous for the crews who risked asphyxiation given that the cab was at the back near the tender.
To deal with this challenge, legend has it that one engineer started running his tunnel-laden route with the locomotive running backward. This meant that the tender was first, so the smoke would be behind him. While this worked in improving the condition of the crew and alleviating the smoke issue, it had other major problems. The tender blocked the view and placed the crew on the wrong side of the tracks, so the crew couldn’t see the signals properly. These tenders had not been designed to be pushed, especially at any speed, so this limited the speed of the train while it ran backwards.
Other train crews soon followed suit, so the SP realized they had to come with a lasting solution. The company teamed up with Baldwin Locomotive Works in 1910 to produce 15 Class MC-2 2-8-8-2s, which was the beginning of the first true Southern Pacific Cab Forwards. These locomotives were numbered 4002 to 4016 and went straight into service without being tested.
What’s the Purpose of the Cab in Front?
Although a cab forward design had been tried in Italy, Southern Pacific was the only major railroad in the United States to adopt cab-forward steam locomotives. The main purpose of the design was to eliminate smoke, heat, and any other form of exhaust from the boiler entering the cab. This proved to be a real improvement from the conventional steam locomotives in which dangerous exhaust fumes could be funneled into the crew cab, especially in the tunnels and snow sheds.
The cab-forward design also offered improved visibility to the crew as they could see further down the track and even survey both sides of the track. This, of course, also enhanced safety in the tunnels, snow sheds, and around curves.
Even though the cab-forward design gave the crew the best visibility of any steam locomotive, the design remained odd and unique. These Cab Forward steam locomotives had various distinguishing features such as stack splitters. These were installed to prevent smoke and heat from damaging the roofs of the wooden snow sheds. There were also drifting valves placed on top of the cylinders, as well as a large “Southern Pacific” emblem placed on the tender.
More importantly, Cab Forward locomotives were designed as oil-burning locomotives. The idea here was to pressurize the oil and water tanks so that both would flow normally even when the locomotive was on uphill grades. In other words, Cab Forward locomotives utilized oil as the primary source of fuel and it had to be piped from the tender to the firebox.
The cab forwards were also the only steam locomotives that released steam exhaust directly into the atmosphere. This became easily recognizable thanks to the “wheeze” sound. And even though the Southern Pacific Cab Forwards were not very different from the standard locomotives, this different design made them a success on the Sierra Nevada mountain ranges. Better still, the different look made them world-famous.
Was the Cab Forward Design Successful?
The cab-forward design played a critical role in alleviating and risks of the crew getting asphyxiated as a result of the dangerous fumes and exhaust entering the cab, especially in tunnels and snow sheds. This design meant that the cab was at the front of the locomotive and so any fumes produced from the boiler couldn’t be funneled into the cab.
Could Cab Placement be Dangerous for the Crew in an Accident?
Although the cab-forward design was immensely successful in solving how large Southern Pacific steam locomotives dealt with the mountainous Sierra Nevada region, the only issue would be in the event of an accident. The fact that the cab was at the front of the locomotive meant that it would be the first part of the train to be affected in the event of a head-on accident or collision.
While such cases were quite rare, there was one fatal accident that occurred when a moving Southern Pacific Cab Forward train hit a flat car on the Modoc Line near Herlong, California.
Southern Pacific Cab Forward Whistles and Horns
Just like in all standard steam locomotives, whistles and horns were an integral part of the Southern Pacific Cab Forwards. They were used to communicate or alert yard workers, train crew, as well as a warning at grade crossings. The whistles codes were standard and were used in all Southern Pacific Cab Forwards.
In addition to the whistles, these Cab Forwards had electric horns that were installed on the rear of the tenders. This allowed a person standing at the rear end of the locomotive to hear any warnings as the whistle, being at the front of the engine, might not be heard in a noisy train yard. Like whistles, horns were important in alerting anyone of the train’s presence.
How many Cab Forwards were Built?
Before the steam locomotive era came to an end in the late 1950s, Southern Pacific had a total of 256 Cab Forwards in various classes (see below). While they were built to provide a lasting solution to the challenging Sierra Nevada terrain, the Cab Forwards easily became a symbol of the Southern Pacific.
The first true Cab Forward locomotives to be ordered from Baldwin Locomotive Works by the Southern Pacific were 15 locomotives (numbered 4002-4016) and were delivered in early 1910. Classed as MC-2 2-8-8-2s, these locomotives proved a success and prompted the company to order 12 more locomotives (numbered 4017-4028) in 1912. These were classed as MC-4 with a wheel arrangement of 2-8-8-2.
20 more 2-8-8-2s were commissioned in 1912. They were classed as MC-6 and brought the total of Southern Pacific Cab Forwards to 47. The company later ordered another 11 2-10-2s Cab Forward units from American Locomotive Company in 1917. This was to help it deal with faster freight schedules, which were dictated by increasing competitive pressures.
The latest units proved so successful that the company ordered another 159 Cab Forward units in the 1920s. But because of the high rail wear and general maintenance costs caused by other forms of wheel arrangements, the company settled on three different wheel arrangements: 2-8-8-2s, 4-6-6-2s, and 4-8-8-2s. The 4-8-8-2s, which were found on class AC-4 through to AC-12 classes of the locomotives built between 1930 and 1942, were more powerful than their predecessors and had more tractive effort.
Every Southern Pacific Cab Forward
|MC-1||4000 – 4001||2-8-8-2||85,040||4,000||Baldwin||1908|
|MC-2||4002 – 4016||2-8-8-2||85,040||4,000||Baldwin||1910|
|MC-4||4017 – 4028||2-8-8-2||85,040||4,000||Baldwin||1911|
|MM-2||4200 – 4211||2-6-6-2||65,900||3,000||Baldwin||1911|
|MC-6||4029 – 4048||2-8-8-2||85,040||4,000||Baldwin||1912|
|AM-21||4200 – 4211||4-6-6-4||76,800||3,450||Rebuild||1914|
|AM-22||3900 – 3911||4-6-6-4||76,800||3,450||Rebuild||1920|
|AC-13||4000 – 4016||2-8-8-2||90,940||4,350||Rebuild||1931|
|AC-24||4017 – 4028||2-8-8-2||90,940||4,350||Rebuild||1917|
|AC-35||4029 – 4048||2-8-8-2||90,940||4,350||Rebuild||1920|
|AC-4||4100 – 4109||4-8-8-2||116,900||5,640||Baldwin||1928|
|AC-5||4110 – 4125||4-8-8-2||116,900||5,640||Baldwin||1928|
|AC-6||4126 – 4150||4-8-8-2||124,300||6,000||Baldwin||1930|
|AC-7||4151 – 4176||4-8-8-2||124,300||6,000||Baldwin||1937|
|AC-8||4177 – 4204||4-8-8-2||124,300||6,000||Baldwin||1937|
|AC-10||4205 – 4244||4-8-8-2||124,300||6,000||Baldwin||1942|
|AC-11||4245 – 4274||4-8-8-2||124,300||6,000||Baldwin||1942|
|AC-12||4275 – 4294||4-8-8-2||124.300||6,000||Baldwin||1942|
NOTES: All locomotives were built by Baldwin Locomotive Works in Philadelphia. Those noted as a Rebuild, were rebuilt in SP Shops by the railroad from a Baldwin-built locomotive.
1 First rebuild (in the SP Shops) by Southern Pacific of the MM-2 Class of Cab Forwards.
2 Second rebuild by Southern Pacific of the MM-2 Class, this time with a renumbering.
3 Rebuilt Class MC-1 and MC-2 into higher horsepower locomotives in the SP Shops
4 Rebuilt Class MC-4 into higher horsepower locomotives in the SP Shops
5 Rebuilt Class MC-6 into higher horsepower locomotives in the SP Shops
A note on SP Class AC-9. These are not Cab Forwards. Built by the Lima Locomotive Works, these 2-8-8-4 locomotives were known by other railroads as a Yellowstone.
End of an Era
Despite being the king of the railroads during their heydays, the introduction of diesel-powered engines in the mid-1950s spelled doom for Southern Pacific Cab Forwards. After conquering the treacherous Sierra Nevada mountain ranges for close to 50 years, the curtain would finally fall for the Southern Pacific Cab Forwards.
The final classes (AC-10, 11, 12) of the legendary SP Cab Forwards were built in the 1940s and operated for a little more than a decade. The last one to run was No 4274 of class AC-10. It pulled a freight from Oakland to Davis on November 30, 1956, in what proved to be the end of a great era.
Any Survivors? The Legendary 4294
Only one of these unique Cab Forward locomotives is preserved. The very last Cab Forward ordered and built, the AC-12 Class member #4294, built in 1944, was spared the scrappers torch. All the rest were scrapped between November 26, 1954, and April 24, 1959. 4294 has been named a “National Historic Mechanical Engineering Landmark“.
Southern Pacific 4294 had been removed from service before the last running Cab Forward retired. Through the efforts of Fred A. Stindt, a member of the Pacific Coast Chapter of the Railway and Locomotive Historical Society, and support from Sacramento civic groups, Southern Pacific agreed to save and donte 4294.
This unique machine was presented to the city of Sacramento on October 19, 1958, and placed on static display next to Southern Pacific’s first-ever locomotive, C. P, Huntington. Highway construction forced 4294 to be brought back to the SP’s Sacramento Shops and placed in storage for 15 years. In 1981 its current home at the California State Railroad Museum, also in Sacramento, was ready to be the permanent home for the last survivor.
A longtime railfan, Bob enjoys the research that goes into his articles. He is knowledgeable on many railroad topics and enjoys learning about new topics. You can get a hold of Bob at his email link below.