Big Boy

1941 · Union Pacific 4000 Class · Work 9 of 1,871

Big Boy, 1941, Union Pacific 4000 Class

A close view along the flank of an enormous locomotive at running board level, two separate sets of cylinders and connecting rods one behind the other driving two groups of tall coupled wheels, the gap between the two engine groups clearly visible, boiler filling the top of the frame, dry desert ballast below.

What it was used for
Union Pacific freight over the Wasatch Range in Utah — 4,000 tons unassisted on a 1.14 per cent grade. Twenty-five built for a wartime traffic that ended in 1945; by the late 1950s none was needed. One of them, 4014, has been running again since 2019.
What was new
The size was not new; doing without the helper engine was. The articulated frame allowed one machine where two had been needed, and saved a crew on every train.

Connections

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

  1. Follows fromChallenger1936Union Pacific's design office under Otto Jabelmann worked from the existing Challengers in the late 1930s: firebox enlarged to 157 square feet, boiler pressure raised to 300 psi, four more coupled wheels, driving wheel diameter cut from 69 to 68 inches.Source: Railway Age, 4. Oktober 1941: ALCO / Union Pacific Wasatch Class Big Boy - Faksimile mit Einführung