Union Pacific Big Boy Class 4884-1 and 4884-2

Union Pacific Big Boy Class 4884-1 and 4884-2.
The Union Pacific railroad required a large locomotive to haul trains over the Wasatch Range without the need to helpers (Banking engines).
The result was the Big Boy manufactured in 1940-1944 by the American Locomotive Company (ALCO) of Schenectady, New York.
There were 25 locomotives built to the 4-8-8-4-wheel arrangement and at 381tons and a length of 85 feet (without tender) were the largest locomotives in the world.
They were not true Mallet locomotives as they used high pressure steam in all cylinders (a true Mallet used compound steam with exhaust steam from the high pressure moving to the low-pressure cylinders).
The locomotives spent a great deal of their working lives on the Wasatch Range and Sherman Hill sections across the Rocky Mountains in the USA.

Union Pacific Number Series Class
4884-1 4000-4019 Class 4884-2 4020-2025 with minor detail differences,
Last withdrawn from service in 1959, 8 have been preserved, one is operational.

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USA Big Boy