Union Pacific Heavy Challenger

Union Pacific Heavy Challengers
Name	Challenger
Number(s)	3950-3969, 3975–3999, 3700-3717
Railway(s)	Union Pacific Railroad
Status	Most scrapped; two preserved
Location	No. 3977: Cody Park, North Platte, Nebraska (static display) No. 3985: Silvis, Illinois, under restoration by Railroading Heritage of Midwest America
Technical specifications
Type	Steam Locomotive
Designer(s)	Otto Jabelmann
Serial number(s)	69760–69779, 70158–70162, 70169–70182, 70678–70683, 72792–72811
Batch number	Five batches, 1942–1944
Manufacturer(s)	American Locomotive Company (ALCO)
Manufacturer(s)	Schenectady Works
Build date	1942-1944
Total produced	71 Units
Supplier of parts	Alco, UP Factory
Classification	4664-3, 4664-4, 4664-5
Model	Challenger (Heavy type)
Wheel arrangement	4-6-6-4
Axles	12
Dia. of Drivers	69 in (1,753 mm)
Dimensions	Length: ~121 ft (36.9 m) including tender Height: ~16 ft (4.9 m)
Weight	Engine: ~566,000 lb (257 t) Tender: ~342,000 lb (155 t)Combined: ~908,000 lb (412 t)
Rail gauge	Standard gauge, 4 ft 8½ in (1,435 mm)
Valve gear	Walschaerts
Valve gear type	Outside, Piston Valves
Motion	Conventional rod drive
Valves	Piston Valves
Cylinders	4 (two per engine set)
Boiler type	Superheated, firetube
Boiler diameter	94 in (2,388 mm)
Boiler pressure	280 psi (1.93 MPa)
Superheater	Type E Superheater
Cylinder type	Simple Expansion
Bore stroke	21 in (533 mm)
Dia. x stroke	32 in (813 mm)
Firegrate area	132 sq ft (12 m2)
Fuel type	Originally coal, several later converted to oil
Fuel capacity	Tender water: 25,000 US gal (95,000 L) Tender fuel: 28 tons coal or ~6,000 gal (22,700 L) oil
Fuel consumption	10 tons of coal or ~2,000 gal of oil per 100 miles under heavy load
Heating area	2,162 sq ft (200.9 m2)
Braking	Westinghouse air brakes (Cast Iron Shoes)
Performance figures
Maximum speed	70 mph (110 km/h)
Continuous power-output	5,000–5,400 drawbar horsepower at 40 mph
Tractive effort	97,352 lbf (433.04 kN)
Factor of adhesion	4.15
Axle load	67,800 lb (30,750 kg) on drivers
Service information
Entered service	1942-1962
Years in-service	Primarily freight, some passenger assignments (Overland Route, South-Central District)
Operator(s)	Union Pacific Railroad
Formation	Challenger articulated locomotives
Operator(s)	Union Pacific
Allocations	Wyoming, Nebraska, Utah, Idaho mainlines
Running numbers	3975–3999 (Heavy subclass), 3700-series (Oil Burning)
Name	Challenger
Liveries	Black with graphite smokebox, later “two-tone gray” for passenger service
Scrapped	Most between 1959–1963
Disposition details
Withdrawn	By 1962
Retired	1962
Preserved	Nos. 3977 and 3985 were preserved
Restored	No. 3985 restored to operation in 1981, retired 2010, undergoing restoration since 2022
Latest overhaul	No. 3985 currently being restored by RRHMA
Disposition	No. 3985 under restoration, No. 3977 on display, remainder scrapped
Number scrapped	69 of 71 units

The Union Pacific Challengers are a type of simple articulated 4-6-6-4 "Challenger"steam locomotives 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 and eventually donated to the Railroading Heritage of Midwest America in 2022, where the locomotive is undergoing a second restoration. The only other surviving Challenger is UP No. 3977, which is on display in North Platte, Nebraska.

History

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. 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 taken over by unassisted Big Boys

Construction

The 105 locomotives were ordered in five batches: the first two of light Challengers, and the final three of heavy Challengers. The Challengers, along with the Big Boys, were introduced just as traffic was surging in preparation for American entry to World War II.

Preservation

Two examples have survived into preservation, those two being Nos. 3977 and 3985.

No. 3977

No. 3977 was built in 1943 as part of the 4664-4 Batch of Heavy Challengers and when it was spared from scrap, it was first relocated to Cody Park in October 1968.

As of today No. 3977 is still on static display in Cody Park.

No. 3985

No. 3985 was built in July 1943 as part of the 4664-4 Batch of Heavy Challengers and was spared from the scrap heap, and was stored with Big Boy No. 4023 where 3985 was restored by a group of employed volunteers in March 1981 and where it ran on excursion service until October 14, 2010. It masqueraded as Clinchfield Heavy Challenger No. 676 (the next member of the Clinchfield Railroad Heavy Challengers), it's fallen sister locomotive No. 3967, and as a What-If Scenario for when it would have been converted to burn oil in the steam era, it was retired on January 2020 and rested until April 2022, it was donated to Silvis Illinois along with TTT-6 No. 5511 and is currently undergoing restoration.

Stock list

4664-3

Status: All Members Scrapped

Image	Loco No.	Build date	Notes
	3950	1942
	3951	1942
	3952	1942
	3953	1942
	3954	1942
	3955	1942
	3956	1942
	3957	1942
	3958	1942
	3959	1942
	3960	1942
	3961	1942
	3962	1942
	3963	1942
	3964	1942
	3965	1942
	3966	1942
	3967	1942	Hauled an excursion train before being scrapped.
	3968	1942
	3969	1942

4664-4

Status: Two Preserved, 3977 and 3985

Image	Loco No.	Build date	Status	Notes
	3975	1943	Scrapped
	3976	1943	Scrapped
	3977	1943	Preserved. On static display in Cody Park
	3978	1943	Scrapped
	3979	1943	Scrapped
	3980	1943	Scrapped
	3981	1943	Scrapped
	3982	1943	Scrapped
	3983	1943	Scrapped
	3984	1943	Scrapped
	3985	July 1943	Undergoing restoration to operating condition.
	3986	1943	Scrapped
	3987	1943	Scrapped
	3989	1943	Scrapped
	3990	1943	Scrapped	Tender was reused in the creation of Union Pacific's GTEL Coal Burner
	3991	1943	Scrapped
	3992	1943	Scrapped
	3993	1943	Scrapped
	3994	1943	Scrapped
	3995	1943	Scrapped
	3996	1943	Scrapped
	3997	1943	Scrapped
	3998	1943	Scrapped
	3999	1943	Scrapped

4664-5

Status: All Members Scrapped

Image	Loco No.	Build date	Notes
	3930	1944
	3931	1944
	3932	1944
	3933	1944
	3934	1944
	3935	1944
	3936	1944
	3937	1944
	3938	1944
	3939	1944
	3940	1944
	3941	1944
	3942	1944
	3943	1944
	3944	1944
	3945	1944
	3946	1944
	3947	1944
	3948	1944
	3949	1944

Gallery

• Gallery

List of Union Pacific Challenger Locomotives
CSA-1:	3900 (3800) • 3901 (3801) • 3902 (3802) • 3903 (3803) • 3904 (3804) • 3805 • 3906 (3806) • 3807 • 3808 • 3909 (3809) • 3910 (3810) • 3911 (3811) • 3912 (3812) • 3913 (3813) • 3914 (3814)
CSA-2:	3815 • 3816 • 3817 • 3918 (3818) • 3819 • 3820 • 3821 • 3822 • 3823 • 3822 • 3823 • 3824 • 3825 • 3826 • 3827 • 3828 • 3829 • 3830 • 3831 • 3832 • 3833 • 3834 • 3835 • 3836 • 3837 • 3838 • 3839
4664-3:	3950 • 3951 • 3952 • 3953 • 3954 • 3955 • 3956 • 3957 • 3958 • 3959 • 3960 • 3961 • 3962 • 3963 • 3964 • 3965 • 3966 • 3967 • 3968 • 3969
4664-4:	3975 • 3976 • 3977 • 3978 • 3979 • 3980 • 3981 • 3982 • 3983 • 3984 • 3985 • 3986 • 3987 • 3988 • 3989 • 3990 • 3991 • 3992 • 3993 • 3994 • 3995 • 3996 • 3997 • 3998 • 3999
4664-5:	3730 • 3731 • 3732 • 3733 • 3734 • 3735 • 3736 • 3737 • 3738 • 3939 • 3740 • 3741 • 3742 • 3743 • 3744 • 3745 • 3746 • 3747 • 3748 • 3749
Clinchfield Railroad:	Locomotive Type
Extinct:	Fetter Challengers
Excursion Star:	3967 • 3985
Preserved:	3977 • 3985