Union Pacific Railroad


This fine locomotive is in 1:16 scale for 3.5” gauge, photographed at the 2018 Alexandra Palace event. It is an articulated Union Pacific Railroad Challenger 4-6-6-4 with cast iron frames and fully equalized suspension. It is paraffin fired.

The American Locomotive Company built 105 of these locomotives between 1936 and 1943. The Challengers were almost 122 ft long, weighed 314 tons and operated over most of the Union Pacific system, mainly hauling freight, but a few were assigned to passenger trains like the Portland Rose. Much of the experience gained later went into the design of the humungous ‘Big Boy’.

The name ‘Challenger’ was given to steam locomotives with a 4-6-6-4 wheel arrangement. Each set of six driving wheels is driven by two steam cylinders. In effect, two engines under one boiler. They were developed to meet a need for higher main-line service speed. Historically, articulated locomotives had been limited to slow speeds by factors inherent in their design.

Technical breakthroughs achieved with the Challenger enabled it and the Big Boy to have speeds in excess of 60mph using around 280 psi boiler pressure, something usually reserved exclusively for passenger locomotives. These locos had 69 inch drivers, usually only found on passenger locomotives.

Photo Mark Evans