Union Pacific No. 3985 is a 4-6-6-4 Challenger built by the American Locomotive Company in July 1943.
The locomotive was one of 105 Challengers built for Union Pacific between 1936 and 1943.
Its articulated layout placed two sets of six driving wheels beneath one boiler, giving the locomotive the ability to produce high tractive effort while still negotiating curves and running at useful road speeds.
No. 3985 worked in regular Union Pacific service until the late 1950s and was retired in the early 1960s.
The locomotive survived because it remained in Cheyenne and was eventually placed on public display rather than being scrapped.
Union Pacific employees began a volunteer restoration that returned 3985 to operation in 1981.
For decades it became one of the most powerful operating steam locomotives in the world and hauled excursion and special trains across the Union Pacific system.
In 1990 the locomotive was converted from coal to oil firing. Railroading Heritage of Midwest America records that the change simplified handling and reduced the risk of trackside fires from coal embers.
Its final Union Pacific operation occurred in 2010. Union Pacific later retired it from active heritage service and donated the locomotive to Railroading Heritage of Midwest America in 2022.
RRHMA is performing a major multi-year restoration at Silvis, Illinois. For TransitSatellite, current status must be time-stamped: 3985 is historically an operating preservation locomotive, but it should not be presented as currently operational until the restoration organization confirms its return to service.