Class 3700 Steam Locomotive

250 years of American independence

Despite spending many years in the shadow of the world-famous “Big Boys,” the “Challenger” locomotives of the Union Pacific Railroad (UP) were no less impressive. During the steam era, the company’s trains had to negotiate steep grades and numerous curves on the vital transcontinental route through the Rocky Mountains. Helper and pusher locos were commonly used, especially on freight trains. In the mid-1930s, the UP was looking for ways to rationalize this laborious and expensive mode of operation. The twelve-coupled, rigid-framed class 9000 locomotives had been pushed to the limits of their design. As a result, the UP developed a mighty articulated loco that was intended to achieve new levels of performance by harnessing two engines. The production order was ultimately awarded to the American Locomotive Company (ALCO), which delivered the first of these mammoth 4-6-6-4 units to the UP in 1936. The six driving axles were powered by four cylinders, while two pilot and trailing axles per engine made it possible to install a truly super-powered boiler and a massive firebox. The front engine was articulated, which enabled excellent performance on curves. From the outset, these gigantic steam locos measuring 37 meters / 121′ in length and weighing over 450 metric tons / 496 short tons acquitted themselves extremely well in service. With an output of 5,000 PS / 4,931 hp and a maximum speed of 110 km/h / 68 mph, they were also used to operate heavy passenger services. This brilliant design soon acquired the name “Challenger,” most likely to convey the fact that this loco, which was considered ultra-modern at the time, was capable of meeting every challenge. The UP ended up purchasing 105 “Challenger” locos, which were delivered as the class 3900 in five groups between 1936 and 1944. The locos built from 1942 onwards were modified versions with a power output boosted to almost 6000 PS / 5918 hp and a larger tender. Six units received smoke deflectors, a two-tone paint scheme (pale gray/medium gray), and oil firing at the factory for use on express trains. From 1941 onwards, the UP also converted many of its coal-fired “Challenger” locos to oil firing. To distinguish these locos from the coal-fired machines, several were reclassified as 3700-3717. Prior to the dieselization of their operating areas, the “Challenger” locos were important pillars of train haulage at the Union Pacific. Based on their high unit numbers alone, they could scarcely be considered as playing second fiddle to the legendary “Big Boys”. In addition, the shorter length of the “Challengers” made them more versatile. For anyone interested in paying tribute to the golden age of American railroads with gigantic steam locos on their model railroad, the “Challenger” is a must-have model, especially since many other railroad companies also purchased this successful UP design. It should also be noted that the preserved “Challenger,” road number 3985, was the largest operational steam locomotive in the world between 1981 and 2010.

Prototype

Union Pacific Railroad (UP) class 3700 “Challenger” heavy American freight steam locomotive in the rebuilt version with an oil tender. This is a version of the locomotive bearing road number 3704. The loco looks as it did during the 1950s.

Model

The model has a digital decoder and extensive sound functions. It also has a controlled high-performance motor. Six axles are powered. The model has traction tires and a smoke generator. The headlight that changes over with the direction of travel, the number boards and the smoke generator will work in conventional operation and can be controlled digitally. The cab lighting can be controlled digitally. Maintenance-free, warm-white LEDs are used for the lighting. The chassis is articulated to negotiate sharp curves. The model has Boxpok wheels. The minimum radius for operation is R2a (261.8 mm / 10-5/16″).
Length over the couplers approximately 23 cm / 9-3/64″.

This model is a cooperative project with Broadway Limited Imports.

The illustration is a digital retouching. Notes for operation: Although the locomotive can be used on curved track with a radius of 261.8 mm / 10-5/16″ or larger, we recommend larger radius curves. Due to the overhang of the long boiler, signals, catenary masts, bridge handrails, tunnel portals, etc., must be installed to provide sufficient clearance on curves. Due to the high weight of the locomotive, the track must be extremely stable. The turntable and transfer table can be traversed by the locomotive but not turned or moved.