The Union Pacific FEF (Four Eight Four), along with the GS-4 is easily one of the most recognizable US steam prototypes still in operation today. The FEF-3 series of steam locomotives was delivered in 1944 and were the last, and some of the largest, steam locomotives delivered for use by the Union Pacific. Operated solely by the Union Pacific, the FEF's (sometimes referred to as "Northerns", due to the NP's being the first to build steam locomotives with the 4-8-4 wheel arrangement) were intended primarily to be passenger locomotives but the UP's large fleet of available diesels meant that the FEF's were put to work in secondary passenger and fast freight service.
Today, FEF-3 #844 (at some times during history also known as #8444 to avoid numbering conflictions with a diesel loco) survives to pull excursion trains as a publicity locomotive for the Union Pacific, and is one the UP's oldest operating locmotives.
Accompanying the "living legend" FEF-3 is always at least one of a pair of Union Pacific Water Tenders, carrying spare water for the steam engine (Water filling stations being a rarity in the diesel era). These unique re-built cars have seen service as both Steam and Gas Turbine Electric fuel tenders before finally settling into their current forms as part of UP's steam heritage fleet where they operate as separate (but always-present) cars.