Locomotive #3985 – Challenger

Union Pacific (UP) #3985 was one of 105 4-6-6-4 Challenger type locomotives owned and operated UP.  Classified as a 4664-4 by the railroad, the locomotive was built by the American Locomotive Company in July 1943 with builder’s number 70174.  It was included in the second order of the second version of Union Pacific’s 4-6-6-4 locomotives.

The locomotive operated in fast freight and passenger service, pulling its last revenue train in 1957 before going into storage and eventual retirement in July 1962.  UP #3985 was chosen for display at the Cheyenne, WY, passenger station and installed there in October 1974.  A group of dedicated UP employees inspected the locomotive with the goal of eventual restoration to service. #3985 was removed from display in September 1979.  The Challenger was returned to service in April 1981, with UP reinstating it to the active roster. On April 23, 1981 it double headed with UP #844 for the first time on a trip for the Grand Opening of the California State Railroad Museum. On June 16, 1982 it embarked on its very first solo trip to Pocatello, Idaho and return.

UP #3985 was converted from coal firing to oil firing in 1990 for ease of operation and to eliminate the tendency of starting lineside fires caused by hot embers from #3985’s stack.  The locomotive burns readily-available diesel fuel which provides for much easier handling than coal and the disposal of the residual ash.

The final operation of the locomotive occurred during an extended tour of a portion of the Union Pacific system that ended on October 14, 2010.  Union Pacific retired the locomotive from active service in February, 2020.

#3985 is only one of two in existence, the other is #3977 in North Platte, NE. In April 2022, Union Pacific officials announced that the company would donate the locomotive to RRHMA, which plans to restore it to operating condition.

Read the complete article on the Union Pacific donation of #3985 here.

#3985 Specifications


Builder – American Locomotive Company (ALCO)
Serial number – 70174
Build date – July 1943

Driver dia. 69 in 
Wheelbase 121 ft 10+7⁄8 in (Engine + tender)
Axle load 67,333 lb
Adhesive weight 404,000 lb
Loco weight 627,900 lb
Tender weight 446,000 lb
Total weight 1,073,900 lb
Fuel type No. 5 fuel oil, originally coal
Fuel capacity 6,450 US gal
Water cap. 25,000 US gal

Firebox:
• Firegrate area 132 sq ft
Boiler 94 in 
Boiler pressure 280 lbf/in2 
Heating surface 4,795 sq ft 
• Tubes 527 sq ft
• Flues 3,687 sq ft
• Firebox 140 sq ft 
Superheater:​
• Heating area 2,162 sq ft
Cylinders – Four – Each 21 in × 32 in