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The Heritage Fleet

The History of the Challengers


Challenger No. 3985

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. In essence, the result 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.

Prior to the Missouri River Eagle/Sedalia Sesquicentennial Special in 2010, No. 3985 had been shop-bound for routine maintenance since 2008. These videos show her first test runs after that down-time.

Train Statistics


Inside Diameter: 94-11/16in.
Pressure:     280 lbs.


Cylinder:     Diameter: 21 in.
Stroke:     32 in.

Driving Wheel Diameter:   69 in.

Evaporating Surfaces (Sq. Ft.):   Tubes: 527
Flues:   3,687
Fire Box:    500
Circulators: 81
Total:   4,795

Factor of Adhesion:   4.17


Fire Box: 

Length: 187-1/32 in.
Width:108-3/16 in.


Fuel:  6,450 gallons No. 5 oil

Gauge of Track:  4 ft. 8-1/2 in.

Grate Area:  Removed, 1990

Maximum Tractive Power:  97,350 lbs.

Superheating Surface (Sq. Ft.):   2,162

Tender Type:  14-wheeled



2-1/4 in. Diameter:  45 x 20 ft. 0 in.
4 in. Diameter:  177

Water Capacity:  25,000 gallons

Weight in Working Order (Lbs.): 

Leading: 102,300
Driving: 404,000
Trailing: 121,600
Engine: 627,900


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

Steam Engine, Locomotive, Heritage Fleet

844 Steam Engine

Steam Locomotive No. 844 is the last steam locomotive built for the Union Pacific Railroad, delivered in 1944. A high-speed passenger engine, it pulled such widely known trains as the Overland Limited, Los Angeles Limited, Portland Rose, and Challenger trains.

Many people know the engine as the No. 8444, when an extra '4' was added to its number in 1962 to distinguish it from a diesel numbered in the 800 series.

The steam engine regained its rightful number in June 1989, after the diesel was retired. When diesels took over all of the passenger train duties, No. 844 was placed in freight service in Nebraska between 1957 and 1959. It was saved from being scrapped in 1960 and held for special service.

The engine has run hundreds of thousands of miles as Union Pacific's ambassador of goodwill. It has made appearances at Expo '74 in Spokane, the 1981 opening of the California State Railroad Museum in Sacramento, the 1984 World's Fair in New Orleans, and the 50th Anniversary Celebration of Los Angeles Union Station in 1989.

Hailed as Union Pacific's "Living Legend," the engine is widely known among railroad enthusiasts for its excursion runs, especially over Union Pacific's fabled crossing of Sherman Hill between Cheyenne and Laramie, Wyoming.

The 844 is housed in the UP steam shop in the Union Pacific Main Yard in Cheyenne WY, which is unfortunately not available to the public.

The Union Pacific Steam Shop not only maintains the No. 844, but also maintains and houses the Challenger No. 3985. The Challenger is the world's largest operating steam locomotive and is the only operating engine of its class in the world today.

Train Statistics


Inside Diameter:  86-3/16 in.
Pressure:  300 lbs.


Diameter: 25 in.
Stroke:32 in.


Driving Wheel Diameter:  80 in.

Evaporating Surfaces (Sq. Ft.): 

Tubes: 2,204
Flues: 1,578
Fire Box: 442
Circulator & Arch Tubes: Removed, 1945

Factor of Adhesion:  4.18


Fire Box: 

Length: 150 1/32 in.
Width:96-3/16 in.


Fuel:  6,000 gallons No. 5 Oil

Gauge of Track:  4 ft. 8-1/2 in.

Grate Area:  Removed, 1945

Maximum Tractive Power:  63,800 lbs.


Superheating Surface (Sq. Ft.):  1,400 square feet


Tender Type:  14-wheeled



2-1/4 in. Diameter: 198 x 19 ft. 0 in.
5-1/2 in. Diameter:  58

Water Capacity: 23,500 gallons

Weight in Working Order (Lbs.): 

Leading: 102,130
Driving: 266,490
Trailing: 117,720
Engine: 486,340

Wheel Base: 

Driving: 2 ft. 0 in.
Engine: 50 ft. 11 in.
Engine & Tender:98 ft. 5 in.

Challenger 844, Steam Engine, Locomotive
Big Boy 4014, Steam Engine, Locomotive
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