Union Pacific Big Boy

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Union Pacific Big Boy
UP Big Boy 4019.JPG
Union Pacific Big Boy #4019 hauling a freight train in Echo Canyon, Utah.
Type and origin
Power type Steam
Builder American Locomotive Company
Build date 1941 (20), 1944 (5)
Total produced 25
 • Whyte 4-8-8-4
 • UIC (2′D)D2′ h4
Gauge 4 ft 8 12 in (1,435 mm) standard gauge
Leading dia. 36 in (914 mm)
Driver dia. 68 in (1,727 mm)
Trailing dia. 42 in (1,067 mm)
Wheelbase 72 ft 5.5 in (22.09 m)
Length Locomotive: 85 ft 3.4 in (25.99 m)
Overall: 132 ft 9 14 in (40.47 m)
Width 11 ft (3.4 m)
Height 16 ft 2 12 in (4.94 m)
Axle load 67,800 lb (30,800 kg)
Adhesive weight 540,000 lb (245,000 kg)
Loco weight 762,000 lb (345,600 kg) (381t)
Tender weight 342,200 lb (155,220 kg) (2/3 load)
Total weight 1,250,000 lb (567,000 kg)
Fuel type Coal
Fuel capacity 28 short tons (25.4 t; 25.0 long tons)
Water cap 25,000 US gal (95,000 l; 21,000 imp gal)
 • Firegrate area
150 sq ft (14 m2)
Boiler 95 in (2,400 mm)
Boiler pressure 300 lbf/in2 (2.1 MPa)
Heating surface 5,735 sq ft (533 m2)
 • Tubes and flues 5,035 sq ft (468 m2)
 • Firebox 720 sq ft (67 m2)
 • Type Type A
 • Heating area 2,043 sq ft (190 m2)
Cylinders 4
Cylinder size 23.75 in × 32 in (603 mm × 813 mm)
Performance figures
Maximum speed 80 mph (130 km/h)[2]
Power output 6,290 hp (4,690 kW) @ 35 mph
Tractive effort 135,375 lbf (602.18 kN)
Factor of adh. 3.99
Operators Union Pacific Railroad
Class 4000–4019: 4884-1
4020–4024: 4884-2
Last run July 21, 1959
Preserved 4004, 4005, 4006, 4012, 4014, 4017, 4018, 4023
  • 17 scrapped
  • 7 preserved for display
  • 1 undergoing restoration to operating condition (4014)
Cost to build US$ 265,000 in 1941, equivalent to $4,314,943 in 2016

Big Boy is the popular name of the American Locomotive Company 4000-class 4-8-8-4 articulated, coal-fired, steam locomotives manufactured between 1941 and 1944 and operated by the Union Pacific Railroad until 1959.

The Big Boy fleet of twenty five locomotives were used primarily in the Wyoming Division to haul freight over the Wasatch mountains between Green River, Wyoming and Ogden, Utah. They were the only locomotives to use a 4-8-8-4 wheel arrangement consisting of a four-wheel leading truck for stability entering curves, two sets of eight driving wheels and a four-wheel trailing truck to support the large firebox.

According to a Union Pacific executive, the 4-8-8-4 series originally was to have been called "Wasatch". One day while one of the engines was being built an unknown worker scrawled "Big Boy" in chalk on its front. With that, the legendary name was born and has stuck ever since.[2]


Union Pacific introduced the Challenger-type (4-6-6-4) locomotives in 1936 on its main line over the Wasatch Range between Green River, Wyoming and Ogden, Utah. For most of the route, the maximum grade is 0.82% in either direction, but the climb eastward from Ogden, Utah 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.

To eliminate the need for double heading and helper operations, Union Pacific decided to design a new locomotive. For such a locomotive to be worthwhile, it would have to be faster and more powerful than slower locomotives like earlier compound 2-8-8-0s that UP tried after World War I. To avoid locomotive changes, the new class would need to pull long trains at a sustained speed of 60 miles per hour (100 km/h) once past mountain grades. In fact, it was designed so that it could travel smoothly and safely at 80 miles per hour (130 km/h) — even though it was not intended to be used that fast.[2]

Led by mechanic Otto Jabelmann, the Union Pacific Railroad's design team worked with the American Locomotive Company to re-examine their Challenger locomotives. The team found that Union Pacific's goals could be achieved by enlarging its firebox to approximately 235 by 96 inches (5.97 m × 2.44 m) (about 155 sq ft or 14.4 m2), lengthening the boiler, adding four driving wheels and reducing the size of the driving wheels from 69 to 68 in (1,753 to 1,727 mm) on a new engine.

The Big Boys are articulated, like the Mallet locomotive design. They were built with a wide margin of reliability and safety, and normally operated well below 60 miles per hour (100 km/h) in freight service. Peak horsepower was reached at about 35 mph (56 km/h); optimal tractive effort, at about 10 mph (16 km/h).

Without the tender, the Big Boy has the longest engine body of any reciprocating steam locomotive.


The American Locomotive Company manufactured 25 Big Boy locomotives for Union Pacific; two groups of ten in 1941 and one group of five in 1944.


The backhead (controls) of 4017 at the National Railroad Museum in Green Bay, Wisconsin

The Big Boy locomotives had large grates to burn the low-quality bituminous coal from Union Pacific-owned mines in Wyoming.

As an experiment, Locomotive 4005 was converted to burn oil; unlike a similar effort with the Challengers, it failed due to uneven heating in the Big Boy's large, single-burner firebox.

Another experiment that took place for a short time was giving locomotive 4019 smoke lifters, similar to those found on locomotive 844.[3] They were later removed for unknown reasons.

Postwar increases in the price of both coal and labor and the efficiency of diesel-electric motive power foretold a limited life for the Big Boys, but they were among the last steam locomotives taken out of service. Towards the end of their career, the Big Boys could still pull more than their rated tonnage of 6,573 short tons (5,963 t). The Big Boys' ratings were increased several times until they regularly pulled 8,727 short tons (7,917 t) over the Wasatch range.

The last revenue train hauled by a Big Boy ended its run early in the morning on July 21, 1959. Most were stored operational until 1961 and four remained in operational condition at Green River, Wyoming until 1962. Their duties were assumed by diesel locomotives and gas turbine-electric locomotives.


On April 27, 1953, Locomotive 4005 was pulling a freight train through southern Wyoming and jumped the switch track at 50 mph (80 km/h), throwing the engine onto its left side and derailing its tender and the first 18 freight cars of the 62-car train. The engineer and fireman were killed instantly on impact and the brakeman died in a hospital a few days later from his severe burns. The cab of the locomotive was destroyed by the tender, and the loads from the 18 derailed cars were scattered near the site of the accident. After this incident, the locomotive was repaired by Union Pacific at its Cheyenne facility.[4]


Of the 25 Big Boy locomotives manufactured, eight remain. Seven of the eight surviving Big Boys are on static display. One, number 4014, is undergoing a restoration to operating condition for excursion service which includes conversion to No. 5 oil firing. Five are displayed outdoors without protection from the elements; 4005 and 4017 are displayed indoors. The remaining Big Boy locomotives are located throughout the United States:

In Popular Culture[edit]

The Galaxy Railways, a 26-episode anime television series tells the story of futuristic galactic society that uses flying trains to travel through the far reaches of space. One of the most important trains in the series known as ‘Big One’ is based on the UP Big Boy. [7]

See also[edit]

Notes and references[edit]


  1. ^ Peck, Combes & Augur 1950, pp. 501,519,523,545.
  2. ^ a b c Elliott, Dan (April 15, 2014). "Huge Big Boy steam locomotive coming back to life". Yahoo! News. Associated Press. Retrieved April 15, 2014. 
  3. ^ http://www.kohs.com/UP_BigBoy_Pages/Prototype%20Photos/UP_BigBoy_4019.htm
  4. ^ "DISASTER ON THE RAILS". Forney Museum of Transportation. Retrieved 16 February 2016. 
  5. ^ a b c Chappell, Gordon. "Union Pacific No. 4012". Steam Over Scranton: Special History Study, American Steam Locomotives. National Park Service. Retrieved March 13, 2012. 
  6. ^ "Steamtown's Locomotives and Cars". Steamtown National Historic Site. National Park Service. Retrieved March 13, 2012. 
  7. ^ http://trainfanatics.com/10-things-you-might-not-know-about-union-pacifics-big-boy/


  • Peck, C. B.; Combes, C. L.; et al., eds. (1950). 1950-52 Locomotive Cyclopedia of American Practice (Fourteenth ed.). New York: Simmons-Boardman Publishing. ASIN B009AF0VKU. 

External links[edit]