Union Pacific Big Boy
The Union Pacific Big Boy is a type of simple articulated 4-8-8-4 steam locomotive manufactured by the American Locomotive Company between 1941 and 1944 and operated by the Union Pacific Railroad in revenue service until 1959.
The 25 Big Boy locomotives were built to haul freight over the Wasatch mountains between Ogden, Utah, and Green River, Wyoming. In the late 1940s, they were reassigned to Cheyenne, Wyoming, where they hauled freight over Sherman Hill to Laramie, Wyoming. They were the only locomotives to use a 4-8-8-4 wheel arrangement: 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.
Today, eight Big Boys survive, with most on static display at museums across the country. One of them, No. 4014, was re-acquired by Union Pacific and restored to operating condition in 2019, regaining the title as the largest and most powerful operating steam locomotive in the world.
History
Design
In 1936, Union Pacific introduced the Challenger-type locomotives on its main line over the Wasatch Range between Green River and Ogden. 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 freight train demanded double heading and helper operations, which slowed service. So Union Pacific decided to design a new locomotive that could handle the run by itself: faster and more powerful than the compound 2-8-8-0s that UP tried after World War I, able to pull long trains at a sustained speed of once past mountain grades.Led by Otto Jabelmann, the head of the Research and Mechanical Standards section of the UPRR Mechanical Department, the UP design team worked with ALCO to re-examine their Challenger locomotives. The team found that Union Pacific's goals could be achieved by enlarging its firebox to about , increasing boiler pressure to 300 psi, adding four driving wheels, and reducing the size of the driving wheels from on a new engine. The new locomotive was carefully designed not to exceed an axle loading of 67,800 lb, and achieved the maximum possible starting tractive effort with a factor of adhesion of 4.0. It was designed to travel smoothly and safely at, even though it was not intended to be used that fast.
To achieve these new engineering goals, the locomotive was "comprehensively redesigned from first principles," wrote locomotive historian Tom Morrison. The overall design simplified some aspects of previous locomotive designs and added complexity elsewhere. Compounding, booster, and feed water heaters were eliminated, as were Baker valve gear and limited cut-off. But the "proliferation of valves and gauges on the backhead showed that running a Big Boy was an altogether more complicated and demanding task for the crew than running previous existing locomotives," Morrison wrote.
The 4-8-8-4 class series, originally rumored to be called the "Wasatch", after the Wasatch Mountains, acquired its nickname after an unknown worker scrawled "Big Boy" in chalk on the front of No. 4000, then under construction as the first of its class.
The Big Boys were articulated, like the Mallet locomotive design, though lacking the compounding of the Mallet. They were built with a wide margin of reliability and safety, and normally operated well below in freight service. Peak horsepower was reached at about. The maximum drawbar pull measured during 1943 tests was 138,000 lbs while starting a train.
The Big Boy has the longest engine body of any reciprocating steam locomotive, longer than two buses. It was likely the heaviest steam locomotive ever built: the engine and tender together outweighed a Boeing 747. There is some speculation that the first series of Chesapeake and Ohio 2-6-6-6 “Allegheny” locomotives, built by the Lima Locomotive Works in 1941, may have weighed as much as, exceeding the Big Boys, but subsequent re-weighs of early-production H8s, under close scrutiny by the builder and the railroad, found them to be less than.
Construction
The American Locomotive Company manufactured 25 Big Boy locomotives for Union Pacific; a group of 20 in 1941 and one group of five in 1944. Along with the Challengers, the Big Boys arrived on the scene just as traffic was surging in preparation for American participation in World War II.| Class | Quantity | Serial Nos. | Year built | UP No. | Notes |
| 4884-1 | 20 | 69571-69590 | 1941 | 4000-4019 | No. 4005 converted to oil fuel in 1946 and reverted to coal in 1948. No. 4019 given experimental smoke deflectors from 1944 to 1945. No. 4014 in excursion service since May 2019. |
| 4884-2 | 5 | 72777–72781 | 1944 | 4020-4024 |
Operation
The Big Boy locomotives had large grates to burn the low-quality bituminous coal supplied by Union Pacific-owned mines in Wyoming. Coal was carried from the tender to the firebox by a stoker motor: a steam engine that drove an Archimedes’ screw.As an experiment, No. 4005 was converted to burn oil in 1946. Unlike a similar effort with the Challengers, the conversion failed due to uneven heating in the Big Boy's large, single-burner firebox. The locomotive was converted back to coal firing in 1948. By contrast, No. 4014 was successfully converted to oil during its restoration. Another short-term experiment was the fitting of smoke deflectors on locomotive 4019, similar to those found on the railroad’s FEF Series, as well as some of their challengers. These were later removed, as the Big Boys' nozzle and blower in the smoke box could blow smoke high enough to keep engineers’ lines of sight clear.
The locomotives were held in high regard by crews, who found them sure-footed and more “user friendly” than other motive power. They were capable machines; their rated hauling tonnage was increased several times over the years. But postwar increases in the price of coal and labor, along with the advent of efficient, cost-effective diesel-electric power, spelled the end of their operational lives. Nonetheless, they were among the last steam locomotives withdrawn from service on the Union Pacific. 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.
In 2019, Union Pacific completed the restoration of No. 4014, and placed it in excursion service. The locomotive was sent on a tour in celebration of the 150th anniversary of the completion of the First Transcontinental Railroad.
Accidents and incidents
- On April 27, 1953, No. 4005 was pulling a freight train through southern Wyoming when it jumped a switch track at, throwing the engine onto its left side and derailing its tender and the first 18 freight cars of its 62-car train. The engineer and fireman were killed on impact; the brakeman died of severe burns in a hospital a few days later. The tender destroyed the cab of the locomotive, and the loads from the 18 derailed cars were scattered. Despite the relatively heavy damage, the locomotive was repaired by Union Pacific at its Cheyenne facility and returned to service.
- On May 16, 2019, No. 4014 partially derailed, with two axles from one set of drive wheels falling into the gauge, while entering the yard at Rawlins, Wyoming; the derailed drive wheels were returned to the rails within three hours.
Preservation