The result of seven years of development focused heavily on efficiency and speed to combat the new diesel-electric locomotives that were on the rise with their unrelenting fuel economy and reduced downtime.
The bed of the firebox and boiler were cast with the chassis as one piece instead of building the locomotive on a riveted frame—much like the difference between a stiff supercar monocoque and a floppy pickup ladder frame. This not only strengthened the 844 as a whole but also reduced its weight significantly, because portions of the drive cylinders and valves, various air channels for the firebox, and the cab floor were integral to the chassis.
This was built to hustle passengers all throughout the Midwest, anywhere from Chicago to Los Angeles, at speeds up to 110 mph. The engine and tender of the 844 weigh almost 1-million pounds (454 tons) along with the added weight of the passenger cars behind it.
By 1960 the diesel-electrics had taken over the passenger routes, and UP attempted to use the 844’s massive boiler as an experimental snow-melter, redirecting steam to jets in front of the locomotive to blast and melt snow off the tracks.