UP (Union Pacific) No. 843 is a type of FEF-3 Class (FEF meaning, "four-eight-four") 4-8-4 'Northern' steam locomotive that was built by ALCO (Schenectady Locomotive Works) in 1944 for the Union Pacific Railroad.
This locomotive was used for passenger and freight service on the Union Pacific Railroad.
The locomotive was retired from service in 1957 and it was sold for scrap.