The 4-8-8-4 Big Boy, Power and Speed

The Big Boy steam locomotive class was a monster and like the B&O’s EM-1 class carried the latest in steam technology being built by the American Locomotive Company in the early 1940s. The development of the Union Pacific Big Boy came about because of a need for more powerful locomotives to move freights between Ogden, Utah and the Wasatch. In an effort to reduce helper service over this stretch of 1.14% grade Union Pacific wanted to employ a single locomotive capable of pulling an entire train by itself to eliminate helper service. What they came up with was the legendary “Big Boy”, a massive 4-8-8-4 design that was capable of producing 135,000 pounds of tractive effort and a boiler pressure of 300 psi. The first Big Boy entered service in September of 1941 and in all Union Pacific would end up with twenty-five of the behemoths numbered 4000-4024.


Laying just a stone's throw east of Ogden are Utah's Wasatch Mountains, a beautiful but quite rugged range that plagued the Union Pacific since it first laid rails westward through the region in the late 1860s.  As part of the railroad's Overland Route main line the stretch of track between Ogden and Wasatch, which saw grades top out at 1.14% for eastbound movements, was quite busy.  In 1936 UP introduced its latest locomotive to tackle the steep grades, its fleet of 4-6-6-4 Challengers designed by A.H. Fetters.  However, even these powerful steamers still required either helpers or doubleheading to move a 3,600-ton train over the mountain, which added to transit times by adding and removing the extra locomotive(s).  Looking for a single unit to do the job UP went to its Department of Research and Mechanical Standards (DoRMS) led by Otto Jabelmann to come up with a new design that was not only powerful but also faster.

Teaming up with the American Locomotive Company (Alco), Jabelmann and Fetters discovered that beefing up the current 4-6-6-4 design would achieve the desired results by increasing the size of the firebox, lengthening the boiler, adding two additional sets of drivers, and shortening the driving wheels from 69 to 68 inches.  Through these changes the new 4-8-8-4 design offered tractive efforts exceeding 135,000 pounds and could operate at speeds of 80 mph (although no Big Boys actually ever reached these speed while in service, it was an added safety factor built in to the locomotive by its designers to assume a safe operation of up to 60 mph).  According to SteamLocomotive.com the first Union Pacific Big Boy was delivered in Omaha, Nebraska from Alco's Schenectady, New York plant at 6 p.m. on September 5, 1941.

Big Boy Specifications

Builder - American Locomotive Company (Alco)

Fuel - 28 tons

Cyclinders(4) - 23.75" x 32"

Water - 25,000 Gallons

Weight - 1,208,000 Pounds

Diameter of Drivers - 68 Inches

Steam Pressure - 300 PSI

Tractive Effort - 135,375 Pounds


Numbered 4000, Union Pacific would go on to roster two distinct classes of 4-8-8-4s listed simply as Class 1 (4000-4019) and Class 2 (4020-4024) with Alco delivering the final locomotive to the railroad in 1944.  Due to nearby mines in Wyoming owned by UP all of the 4-8-8-4s burned coal although as an experiment #4005 was briefly converted to an oil-burner, which proved unsuccessful.  The Big Boys went on to not only tackle the grades east of Ogden but also worked the Wyoming Division over fabled Sherman Hill east of Lamarie.  Because the diesel was already making its presence known as a main line locomotive when the Big Boy was developed the steamer saw a short lifespan, despite being one of the technologically advanced of its kind ever built. 

The last revenue run of a 4-8-8-4 occurred on July 21, 1959 although the railroad continued to store four, serviceable at Green River, Wyoming through September of 1962.  In any event, most 4-8-8-4s barely saw 20 years of service before retirement, a very young steam locomotive when compared to some still operating today that were built near or over 100 years ago. The Union Pacific Big Boy is often mentioned as the largest steamer ever built, sometimes even saying that they are the most powerful. While in some areas that is the case, in others it is not especially in regards to the overall power it exerted. For example, the Norfolk & Western Y6 and C&O H-8 designs, themselves monsters, were more powerful and larger than the Big Boy in the areas of tractive effort, weight, length and horsepower.

In any event, while the “largest” and “most powerful” steam locomotive will likely always be debated by railfans and historians one thing which cannot be argued is how fortunate this locomotive was compared to other large locomotives like it in regards to preservation. No less than eight of these monsters have been saved and are currently scattered about the country in various parks. They include numbers; 4004-4006, 4012, 4014, 4017, 4018, and 4023.   While perhaps the size of the Big Boy will prohibit even the preservation-minded Union Pacific from operating one of them over its system, as it currently does with its originally owned Challenger #3985 and UP #844 (the only steam locomotive in America to never be retired from active service), it is nevertheless good to see that so many Big Boys have been preserved for future generations to have a glimpse at these truly mighty locomotives.



Finally, as incredible as it seems news leaked on December 7, 2012 that Union Pacific was contemplating restoring a Big Boy back into operating condition for the railroad's 150th celebration in 2019.  Its current target is #4014, owned by the Southern California Chapter of the Railway & Locomotive Historical Society, although UP has supposedly expressed interest in other Big Boys if a deal to acquire #4014 cannot be reached.  The locomotive currently sits on display at the Los Angeles County Fairplex in Pomona, California and was chosen due to its excellent condition (considering its age).  In any event, we will likely not know until sometime in the spring of 2013 if #4014 will be the chosen candidate.

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