Challenger

1936 · Union Pacific 3900 Class · Work 10 of 1,871

Challenger, 1936, Union Pacific 3900 Class

An articulated locomotive with two groups of six coupled driving wheels beneath a single long boiler, the leading group swung out of line on a tight curve, pine slopes rising steeply on the inside of the bend.

What it was used for
Fast Union Pacific freight and passenger trains over the Rocky Mountains.
What was new
Articulated locomotives were held to be slow. This one ran at 70 mph and showed the type was not confined to drag work — the precondition for the Big Boys that grew out of it.

Connections

Every connection names its kind. “Forerunner” on its own would be a claim.

  1. Made possibleBig Boy1941The 4-8-8-4 was not a fresh design but an enlargement of this one. In 1940 Union Pacific and ALCO took the frames and engine units of the 4-6-6-4 as their starting point and added a coupled axle to each unit.Source: Railway Age, 4. Oktober 1941: ALCO / Union Pacific Wasatch Class Big Boy - Faksimile mit Einführung