Trackside Classic: Southern Pacific AC12 Class 4-8-8-2 – A Different Way Forward

Driving a steam locomotive may look glamourous, but the environment isn’t. You’re either too hot or too cold, depending on the season; you get choked by steam and smoke and coal dust; you struggled to see forward and observe signals clearly as boilers grew ever larger and longer; and then there’s the noise and hard ride. So it is perhaps surprising how little effort was made over the years to improve things.

Things evolved slowly. This is Stephenson’s Rocket, of 1829, the first proper steam locomotive. Now you know why the British term isn’t cab, but footplate (still). The footplate is exactly that, there is no cab.

By 1870, the cab had appeared in Britain, but in a very nominal way. This is the ‘Stirling Single’ of the Great Northern Railway, which hauled the fastest expresses of its day. Not a lot of shelter or protection here, and it was anther 50 years before seats were standard..

America moved faster, as the harsher climate demanded, and more generous size of engines allowed larger cabs. In 1869, when the Overland Route, the first transcontinental railroad, was completed at Promontory Point, Utah, the engines had cabs that looked better than anything in Britain until the 1920s – this is a replica of the Central Pacific’s Jupiter. Incidentally, Promontory Point is well worth a visit.

The Overland Route was the work of the Union Pacific, building east from Omaha, Nebraska, and the Central Pacific (which became part of the Southern Pacific (SP) in 1885) building eastward from San Francisco. The SP’s half was obviously the shorter one – but it was the hard part to build and operate. The defining part was (and still is) the crossing of the Sierra Nevada mountains in California, where the line rises to over 7,000 ft. Steep grades on both sides combined with some of the most severe weather in the north America made it probably the most challenging piece of railroad in north America.

Once the line was open, it quickly experienced winter problems. The sheer volume of snow – up to 40 ft can fall in a winter, and then freeze solid, meant the line needed protection The first snowsheds were built as early as 1867. These were basically wooden tunnels, and eventually covered over 40 miles of the Donner Pass. They did the job, and significantly reduced the likelihood of the line being closed by snow.

But the snow sheds had two downsides. Passengers missed 40 miles of scenery, and, more importantly for the SP, the working conditions for engine crews in the sheds were appalling. Imagine being the crew on the second locomotive of a heavy, slow freight train clawing its way up a 2% grade for 80 miles – 40 of those miles in a snow shed. Beyond unpleasant, it was dangerous for the crew, and dangerous for the train as the forward view in a smoke filled tunnel was almost non-existent. And, by 1900, traffic had exceeded the capacity of the route. The SP clearly needed something more than 2-8-0 freight engines to tame Donner.

In 1874, a Swiss engineer Anatole Mallet (1837 – 1919, pronounced Mal-ay, not Mal-et) patented an articulated compound locomotive. A Mallet has two sets of driving wheels, driven by separate pairs of cylinder – high pressure at the rear and low pressure at the front, using the steam from a boiler the length of both sets of wheels in sequence. The rear set of driving wheels were fixed to the frame in the conventional manner, and the front set are attached by a truck that allows the front to turn separately, allowing the engine to navigate tight curves whilst generating the power of two contemporary engines.

ALCO built the first American Mallet for the Baltimore and Ohio Railroad in 1903; it was an 0-6-6-0, and was soon being copied by other railroads and builders.

The SP took notice, and in 1909, the Baldwin Locomotive Company of Philadelphia built SP no 4000 and 4001, of class MC-1 (Mallet Consolidation – Consolidation being the term used for a 2-8-0). These were huge machines – weighing over 180 tons, with a tractive effort of over 90,000 lbf, and intended to replace pairs of 2-8-0s on heavy Donner Pass freights, and thereby eliminate the breathing problems faced by engine crews.

It was a mixed success. Yes, it could haul the trains unaided, but the crews still needed respirators in the snowsheds, and the great length made forward visibility difficult. It isn’t clear who decided to try using the engine in reverse – some say it was an official experiment, others that a fed up driver did it off his own bat. Whichever is true (and it may be both), the experiment succeeded in showing how to solve the smoke problem, leaving the challenge of re-configuring the engine to put the crew at the front, while leaving the tender at the rear – something only possible if the engine was oil-fired. And, very quickly after 4000, no 4002 (class MC-2) emerged from Baldwin’s works in late 1909, looking like no steam engine that had gone before.

4002 was mechanically very similar to 4000, but was configured backwards. The cab was now at the front of the engine, perched in front of a rearward facing firebox, with the smokebox facing backwards to the tender. The cab was a fully closed affair, with large front and side windows. The driver sat on the left, with the controls beside him, and the fireman on the left, with his levers for controlling the supply of oil from the tender to firebox. As it was a Mallet, the steam pipes required for the two sets of cylinders plus the oil supply from back to front gave a very complex and (to British eyes, at least) not particularly aesthetic appearance. But it solved the smoke in snowsheds problem!

By 1915, the SP had 46 cab-forwards, in classes MC-2, -4 and -6. In addition, the concept had been applied to passenger engines, in the 2-6-6-2 MM-2 (Mallet Mogul – a 2-6-0 being a Mogul) class, also from Baldwin. These were soon rebuilt as 4-6-6-2, to give greater control and stability at the leading end.

The Mallets succeeded in their original task – they comfortably replaced double-headed 2-8-0s on Donner Pass freights, but were not perfect. The compound design made them better suited to slow speed, and they struggled to get trains over 25 mph.

So, in the late 1920s, the MM-2s were withdrawn, and then rebuilt in the 1930s, as traffic recovered from the Great Depression, as AM-2 (Articulated Mogul) – the compounding was removed, and the high and low pressure cylinders were replaced with four uniformly sized ones. This was intended to simplify maintenance and thus reduce costs, and the rebuilds were faster.

Similarly, the MC-4 and MC-6 classes were rebuilt as simple engines, and from the AC-4 class of 1928 onwards, all new cab forwards were built as simples. The AC-4 increased tractive effort to 116,000 lb ft, or 5,640hp. The AC-8 of 1939 featured larger cab windows with a pointed prow, which was painted silver for added visibility – and made the cab forwards among the most dramatic looking American steam engines.

The climax of the cab forward was the very similar AC-10, AC-11 and AC-12 classes, of 1942-44. Although still a Baldwin 4-8-8-2 with four cylinders and oil firing, weight was over 500 tons and power was up again, to 124,000 lb ft and 6,000hp – more than frontline GE or EMD diesels, which are around 4,400hp.

The last cab forward built was also SP’s last new steam locomotive – AC-12 no 4294, into service in March 1944. She is now the only one in existence, as the SP allowed all the others to go for scrap as service finished in the early 1950s. Withdrawn in 1956, 4294 now has prime position at the California State Railroad Museum in Sacramento, facing her nemesis, an EMD F7 diesel.

Inside the cab, 4294 and her sisters were very different to conventional engines. This is the fireman’s forward facing seat (above), and the view from the driver’s on the right hand side (the door is open).

The later Cab Forwards were not confined to freight services –they were capable of 70 mph, and regularly hauled the Overland Route expresses, and at times assisted the diesel streamliners that began to appear in the late 1930s.

Ultimately, the SP and Baldwin built 256 cab forwards, and used them on other routes in California as well as the Overland Route. Here, some of the fleet rest at Roseville, between San Francisco and Sacramento.

Much of the complex maintenance was handled at the SP’s shops at Sparks, Nevada

The last cab forward crossed Donner Pass in 1957; the days of steam on the SP were ending, and the new diesels were taking over, including the Alco PA in the stunning ‘Daylight’ colour scheme.

Later, the SP preferred EMD products, such as these F7s in the ‘Black Widow’ colour scheme, before being taken over by Union Pacific in 1996. But the F7 and its stablemates were standard American motive power –not the unique ingenuity and drama of the cab forwards.

Snow remains a challenge on Donner to this day, and the SP also had a large fleet of rotary snowploughs in the Sierras. Wouldn’t you love to see that in action? Union Pacific still keeps them in reserve.

But on occasion, even they were not enough; in January 1952, the City of San Francisco streamliner was trapped on Donner Pass by snowdrifts for 3 days.

The SP wasn’t the only railroad concerned enough about engine crew visibility to try new ideas; it was one of the drivers behind the ‘Camelback’ layout. Moving the driver to a cab mounted centrally above the boiler not only boosted his view, but also created space for a firebox that spanned the full width of the chassis, with a vestigial footplate for the poor fireman. The Central Railroad of New Jersey was a particular fan of this layout, and owned over 300. The type was eventually banned on safety grounds.

To see a cab forward today, you need to head to Sacramento, and the wonderful California State Railroad Museum – probably second only to Britain’s NRM for the telling of the railway story. AC-12 no 4294 has pride of place there, and if you ask nicely, they’ll let you in the cab – it really is something else. And while you’re in town, you’ll also want to visit the California Auto Museum (again?) – volunteer run, with a great collection and great guys showing you round.