The History of the Challengers 
Union Pacific Challenger No. 3985 was designed by Union Pacific
and built in 1943 by the American Locomotive Company. It is one of 105
Challengers built for Union Pacific between 1936 and 1943 and is the only
operating engine of its class in the world today--the largest and most powerful
operating steam locomotive.
No. 3985 last operated in "regular" train service in 1957. It was retired in 1962 and stored in the roundhouse in Cheyenne, Wyoming, until 1975, when it was placed on display near the Cheyenne depot. A group of Union Pacific employees volunteered their services to restore the locomotive to running condition in 1981.
The name Challenger was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading "pilot" truck, which helps guide the locomotive into curves; two sets of six "driving" wheels, and finally, four "trailing" wheels, which support the rear of the engine and its massive firebox. Each set of driving wheels has its own steam cylinder. The result, in essence, is two engines under one boiler.
The frame of the locomotive is "articulated," or hinged, to allow it to go through curves. When watching the approaching locomotive go through a curve, you can see the boiler swing out left or right independently of the lower half of the engine, as the rear half of the locomotive remains in a straight direction until its wheels and frame are halfway through the curve.
The Challengers were designed for fast freight service, but occasionally pulled passenger trains. No. 3985 originally burned coal and pulled a tender with a 32-ton capacity. In 1990, it was converted to use No. 5 oil. The top speed of No. 3985 is about 70 miles an hour.
Additional information on the Challengers and other steam
locomotives can be found in the Historical UP
Locomotives section.
Vital Statistics:
| Tender Type: | 14-wheeled |
| Water Capacity: | 25,000 gallons |
| Fuel: | 5,945 gallons No. 5 oil |
| Gauge of Track: | 4 ft. 8-1/2 in. |
| Cylinder: | Diameter: 21 in. Stroke: 32 in. |
| Driving Wheel Diameter: | 69 in. |
| Boiler: | Inside Diameter: 94-11/16 in. Pressure: 280 lbs. |
| Fire Box: | Length: 187-1/32 in. Width: 108-3/16 in. |
| Tubes: | 2-1/4 in. Diameter: 45 x 20 ft. 0 in. 4 in. Diameter: 177 |
| Wheel Base: | Driving: 12 ft. 2 in. & 12 ft. 2 in. Engine: 60 ft. 4-1/2 in. Engine & Tender: 121 ft.10-7/8 in. |
| Weight in Working Order, Pounds: |
Leading: 102,300 Driving: 404,000 Trailing: 121,600 Engine: 627,900 Tender: 441,900 |
| Evaporating Surfaces, Square Feet: |
Tubes: 527 Flues: 3,687 Fire Box: 500 Circulators: 81 Total: 4,795 |
| Superheating Surface, Square Feet: |
2,162 |
| Grate Area: | Removed, 1990 |
| Maximum Tractive Power: | 97,350 lbs. |
| Factor of Adhesion: | 4.17 |