Union Pacific Challenger
Union Pacific 3985 runs through Alton, Iowa, on October 1, 2008
Type and origin Power type Steam Designer CSA Class : Arthur H. Fetter 4664 Class : Otto Jabelmann Builder American Locomotive Company (ALCO) Build date 1936–1944 Total produced 105 + (6 Denver & Rio Grande Western)
Specifications Configuration: ​  • Whyte 4-6-6-4  • UIC (2′C)C2′ h4g Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Driver dia. 69 in (1,753 mm) Wheelbase 60 ft 4+1⁄2 in (18.402 m) Engine 121 ft 10+7⁄8 in (37.157 m) Engine + tender Adhesive weight 4664-3/4 : 403,700 lb (183,115 kg) 4664-5 : 406,200 lb (184,249 kg) CSA-1/2 : 399,840 lb (181,364 kg) Loco weight 4664-3/4 : 627,000 lb (284,000 kg) 4664-5 : 634,500 lb (287,800 kg) CSA-1/2 : 566,950 lb (257,160 kg) Tender weight 4664-3/4 : 436,500 lb (198,000 kg) 4664-5 : 434,500 lb (197,086 kg) CSA-1/2 : 322,600 lb (146,329 kg) Total weight 4664-3/4 : 1,063,500 lb (482,400 kg) 4664-5 : 1,069,000 lb (484,890 kg) CSA-1/2 : 889,550 lb (403,493 kg) Fuel type Coal, oil Fuel capacity 32 short tons (29 t; 29 long tons) 6,450 US gal (24,400 L; 5,370 imp gal) UP3985 Water cap. 25,000 US gal (95,000 L; 21,000 imp gal) Firebox: ​  • Grate area 4664 Class : 132 sq ft (12 m2) (grate removed in 1990) CSA-1/2 = 108.25 sq ft (10 m2) Boiler 94 in (2,400 mm) Boiler pressure 4664-3/4/5 : 280 lbf/in2 (1.93 MPa) CSA-1/2 : 255 lbf/in2 (1.76 MPa) Heating surface 4,795 sq ft (445.5 m2) ​  • Tubes 527 sq ft (49.0 m2)  • Flues 3,687 sq ft (342.5 m2)  • Firebox 4664-3/4 : 602 sq ft (55.9 m2) 4664-5 : 602 sq ft (55.9 m2) CSA-1/2 = 548 sq ft (50.9 m2) Superheater: ​  • Heating area 2,162 sq ft (200.9 m2) Cylinders Four Cylinder size 4664-3/4/5 : 21 in × 32 in (533 mm × 813 mm) CSA-1/2 : 22 in × 32 in (559 mm × 813 mm)
Performance figures Maximum speed 70 mph (110 km/h) Tractive effort 4664-3/4/5 : 97,352 lbf (433.04 kN) CSA-1/2 : 97,305 lbf (432.83 kN) Factor of adh. 4664-3/4 : 4.15 4664-5 : 4.17 CSA-1/2 : 4.11
Career Operators Union Pacific Railroad Class CSA-1, CSA-2, 4664-3, 4664-4, 4664-5 Preserved Two (Nos. 3985 and 3977) Restored No. 3985; April 1981 Disposition No. 3985 under restoration, No. 3977 on display, remainder scrapped

The Union Pacific Challengers are a type of simple articulated 4-6-6-4 steam locomotive built by American Locomotive Company (ALCO) from 1936 to 1944 and operated by the Union Pacific Railroad until the late 1950s.

A total of 105 Challengers were built in five classes. They were nearly 122 ft (37 m) long and weighed 537 short tons (487 tonnes). They operated over most of the Union Pacific system, primarily in freight service, but a few were assigned to the Portland Rose and other passenger trains. Their design and operating experience shaped the design of the Big Boy locomotive type, which in turn shaped the design of the last three orders of Challengers.

Two Union Pacific Challengers survive. The most notable is Union Pacific No. 3985, which was restored by the Union Pacific in 1981, then operated in excursion service as part of its heritage fleet program. Mechanical problems forced it out of service in October 2010; it was retired in January 2020 after the restoration of the 4-8-8-4 Big Boy 4014^[1][2] and eventually donated to the Railroading Heritage of Midwest America in 2022, where the locomotive is undergoing a second restoration.^[3] The only other surviving Challenger is UP No. 3977, which is on display in North Platte, Nebraska.

History

Description

The name "Challenger" was given to steam locomotives with a 4-6-6-4 wheel arrangement: four wheels in the leading pilot truck to guide the locomotive into curves, two sets of six driving wheels, and four trailing wheels to support the rear of the engine and its massive firebox. Each set of driving wheels is driven by two steam cylinders. In essence, the result is two engines under one boiler. Union Pacific developed five types of Challengers: the "light" CSA-1 and CSA-2 classes and the "heavy" 4664–3, 4664–4, and 4664-5 classes.

The railroad sought powerful locomotives that could handle mountain grades at high speeds. Previously, articulated locomotives had been limited to slow speeds by their design. Technical breakthroughs allowed the UP Challengers to operate with 280 lbf/in² (1.93 MPa) boiler pressure, something usually reserved for passenger locomotives like the FEF Series. They had 69-inch (1,800 mm) drivers, mammoth wheels usually seen on passenger locomotives only because freight engines normally require the extra torque provided by smaller wheels.^{[clarification needed]} Speeds in excess of 60 miles per hour (100 km/h), while unheard-of on most other railroads using articulated steam locomotives, became commonplace on the Union Pacific.

When the first Challengers entered service in 1936, on the UP's main line over the Wasatch Range between Green River and Ogden, the locomotives had problems climbing the steep grades. For most of the route, the maximum grade is 0.82% in either direction, but the climb eastward from Ogden, into the Wasatch Range, reached 1.14%. Hauling a 3,600-short-ton (3,300 t; 3,200-long-ton) freight train demanded double heading and helper operations, and adding and removing helper engines slowed operations. Those limitations prompted the introduction of the Big Boy in 1941, as well as a redesign of the last three orders from 1942 to 1944.

Using the experience from the Big Boy, UP chief mechanical engineer, Otto Jabelmann, redesigned the last three orders of Challengers in 1941. The result was a locomotive in working order weighing some 317 short tons (288 t; 283 long tons) accompanied by a tender weighing 174 short tons (158 t; 155 long tons) when 2/3 loaded. Calculated tractive effort is 97,350 lbf (433.0 kN). From 1941, the Challengers were intended to speed up freight operations on the grades across Wyoming; the Wasatch Range climb east from Ogden was to be conquered by the Big Boys without helpers.

Construction

The 105 locomotives were ordered in five batches: the first two of light Challengers, and the final three of heavy Challengers. Along with the Big Boys, the Challengers arrived on the scene just as traffic was surging in preparation for American participation in World War II.

As part of Union Pacific's fourth order in 1943, ALCO built thirty-one locomotives for Union Pacific using the same specifications. However, the War Production Board diverted six locomotives after completion to the Denver and Rio Grande Western Railroad via a lease through the War Department's Defense Plant Corporation. Locomotives 3900-3905 formed the Rio Grande's Class L-97.^[7] These were later sold to Clinchfield Railroad in 1947 and were renumbered as 670–675, where they formed the Clinchfield's Class E-3; these six Challengers were eventually retired in 1953.^[8]

Preservation

Only two Challengers survive, both from the 4664-4 order built in 1943. No. 3977 is on static display in North Platte, Nebraska. No. 3985 was restored to operating condition by Union Pacific in 1981 and used in excursion service until mechanical problems sent it back into storage in October 2010. It was officially retired in January 2020 and stored in Cheyenne, Wyoming, but has since been acquired by the Railroading Heritage of Midwest America (RRHMA) in Little Silvis Shops in Silvis, Illinois, where the locomotive is now being restored to operation once again.^[9][3]

Surviving Challenger locomotives

Type	Number	Image	Date built	Serial number	Location	Coordinates	Notes
4664-4	3977		June 1943	70160	Cody Park, North Platte, Nebraska	41°08′52″N 100°45′11″W / 41.147853°N 100.753113°W / 41.147853; -100.753113 (Challenger 3977)	Was renumbered to 3710 in 1952.
4664-4	3985		July 1943	70174	Railroading Heritage of Midwest America, Silvis, Illinois	41°7′46.9308″N 104°48′49.1688″W / 41.129703000°N 104.813658000°W / 41.129703000; -104.813658000 (Challenger 3985)	No. 3985 was restored in 1981 and used by Union Pacific on excursions until October 14, 2010, when mechanical problems forced it from service. It was officially retired from UP excursion service in January 2020. In April 2022, No. 3985 was donated to the RRHMA. In November 2022, the locomotive was sent to the RRHMA's workshops in Silvis, IL.[9][3] Restoration work began in January 2023.[10]