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Five Facts You Might Not Know About the Big Boy

We all know the old, tried, and sometimes true saying “Bigger is Better.” Yes, a significantly enlarged bowl of ice cream on a hot summer day is for sure better. Finding out that your car repair bill is larger than anticipated … well, not so good.

In the late 1930s, bigger was better in the eyes of the Union Pacific Railroad—especially when it came to a new locomotive for the Wasatch Mountains.

Located in eastern Utah, the Wasatch Mountains present a formidable barrier along the Union Pacific route. If one travels east from Ogden, Utah for 55 miles, you will be in the little town of Emory, Utah. You will have also gone up 1,900 feet in elevation. This is a beautiful trip up into the mountains driving on the highway. A train, however, is going to struggle with such a steep slope.

Because of the steep slopes, a traffic bottleneck was forming on the Union Pacific line in the Wasatch Mountains. With World War II looming on the horizon, the bottleneck became a significant challenge that needed attention. The answer was a single locomotive that could pull a 3,600-ton train, unassisted, over this stretch. Big Boy was that locomotive. A massive machine measuring nearly half a football field long and weighing in at over 600 tons, Big Boy easily surmounted the Wasatch.

Union Pacific ordered 25 Big Boys. Today, eight remain; the balance having been cut up for scrap. Let’s get to know Big Boy a bit better through five interesting ideas that you might not have realized.

  1. Are you really the biggest? To herald the railroad’s activities during World War II and highlight their new locomotives, the Union Pacific placed full-page ads in national magazines touting the Big Boys as the world’s largest steam engines. Depending on how you want to measure the Big Boys, this statement is both true and false. Judging by weight, Big Boy is very heavy. However, if one considers tractive effort — pulling power — locomotives from the same era built for Chesapeake & Ohio, Great Northern, Norfolk & Western, Duluth, Missabe & Iron Range, Northern Pacific, Erie and Virginian railroads all, on paper, theoretically delivered more power than a Big Boy. This argument goes back and forth. One statistic leans toward the Big Boys, other statistics point elsewhere. Whichever way you look at it, the Big Boys were very large and easily handled the job for which they were built.


  1. How many miles? Union Pacific placed two orders for Big Boys. In 1941, they ordered 20. In 1944, five more were constructed. Their territory was basically the 435 miles between Cheyenne, Wyoming and Ogden, Utah. As a class, Big Boys ran until 1959, with some coming out of service earlier. Additionally, from 1941 to 1948, Big Boys only worked the 163 miles from Ogden to Green River, Wyoming. From 1948 to 1959, they did not travel west of Green River. In their final years, the Big Boys only worked the 58 miles between Cheyenne and Laramie, Wyoming. Every one of the first 20 Big Boys tallied over one million miles of service. The last five had all traveled over 800,000 miles when they were retired. All this on a piece of railroad just over 400 miles long. For the record, #4017 traveled 1,052,072 miles during its life.


  1. Mismatched Tenders! This is trivia, but when you think about it, it makes sense. The tender — the coal car right behind the locomotive — currently on exhibit with #4017 at the National Railroad Museum is not original to the locomotive. One might think that the tender that came with the locomotive from the factory would be the one used throughout it life. Not so. When a locomotive went into the shop for major service, it was separated from its tender. The tender went to one shop building; the locomotive to another. The maintenance on the tender generally took less time than that on the locomotive. When a locomotive came out of the shop, which ever tender was ready to go; that’s the one that was attached. This practice was common in the 1950s, as the Big Boy’s neared the end of their service.

So which tender is behind #4017 at the National Railroad Museum? A small builder’s plate located on the right rear side indicates tender 25-C-404. The important number here is the 404, indicating the tender was the fourth in the second order of Big Boys. Hence it originally belonged to Big Boy #4023.


  1. Speed … The first order of Big Boys, #4000 – 4019, weighed in at 1.18 million pounds in full working order. They were tested at speeds between 70 and 80 m.p.h. In regular service, Big Boys were limited to a top speed of 55 m.p.h. That is a very large mass of iron coming down the tracks at a very high speed. From the time the engineer applied the brakes, until the time the Big Boy and train came to a complete stop was between 1 to 1.5 miles


  1. A BIGGER Big Boy? Finally, as if the 4000s weren’t big enough, the Union Pacific actually contemplated ordering five additional 4-8-8-4s that would be even larger. As World War II dragged on, the U.P. needed additional power on its line to Los Angeles through southwest Utah. According to an article by historian and artist Gil Bennett (Classic Trains, Spring 2019), plans were on the drawing board to build #4025-4029. This third class of Big Boys was to measure 139 feet, 11 5/8 inches long and weighs just under 1.3 million pounds. All would be oil fired, instead of coal. The locomotive, itself, would be a foot longer than existing Big Boys. The tender was to be extended to just over 54 feet long in order to accommodate a 33,000 gal. water tank. By comparison, #4017 is 132 feet, 9 7/8 inches long. Its water tank holds 24,000 gals. When the war ended in September 1945, at least a year, if not two, ahead of some predictions, the need for extra steam powered locomotives became a moot point. The bigger Big Boy idea was dropped and the Union Pacific, like most other major railroads, concentrated on shifting to diesel power.



Author: Bob Lettenberger, Education Director

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