Union Pacific “Big Boy” No. 4012 on display at Steamtown National Historic Site
See the Train Collection web page for more locomotives at Steamtown National Historic Site.
Note: Numbers used in this article, such as 4-8-8-4, are known as Whyte Notation. This is a system to classify steam locomotives that was created by Frederick Whyte in 1900. These numbers describe the arrangements of wheels. Most locomotives only have three numbers, with the first being the number of non-powered wheels used to support the front of the engine, the second being the number of powered wheels, and the third being the number of non-powered rear wheels. For locomotives with four or more numbers in their Whyte Notation, the first and last numbers are always the front and rear non-powered wheels, while all others are groups of powered wheels.
Twenty-five “Big Boy” locomotives were manufactured in Schenectady, New York, by the American Locomotive Company between 1941 and 1944 exclusively for the Union Pacific Railroad. Only eight survive today, one of which is now prominently on display at Steamtown National Historic Site following a cosmetic restoration that was completed in 2021. The locomotive is typically open to visitors between certain hours, and a park Ranger is on board to answer any questions.
Ranger gives a lecture inside the cab of Union Pacific “Big Boy” No. 4012 on display at Steamtown National Historic Site
The Big Boys are some of the largest and most powerful steam locomotives ever built. How powerful are they? It would take four modern diesel engines to pull a five-mile long train. A Big Boy could do this on its own. How big are they? The locomotive and tender weigh roughly 600 tons. Typical steam locomotives and tenders weigh between 100 and 300 tons. Big Boy’s tender, which is as large as many of the steam engines on display at Steamtown National Historic Site, holds 24,000 gallons of water and 28 tons of coal.
Tender car of the Union Pacific “Big Boy” No. 4012 on display at Steamtown National Historic Site
Furthermore, Big Boys are the only 4-8-8-4 locomotives ever produced. As the Whyte Notation indicates, the Big Boys had two sets of powered wheels. Four wheels (four on each side makes 8) are joined together by coupling rods, and there are two sets, thus the 8 and 8 in the classification number.
Set of powered wheels on the Union Pacific “Big Boy” No. 4012 on display at Steamtown National Historic Site
No. 4012 was delivered to Union Pacific in 1941, and like all Big Boys, it was deployed out west to haul freight between Cheyenne, Wyoming, and Ogden, Utah. The mountains in that area required two Challenger-type 4-6-6-4 engines to pull a typical load. A Big Boy could do the work by itself.
Union Pacific No. 4012 remained in operation until 1962, at which time diesel locomotives took over the industry. It was then donated to Steamtown USA. In fact, Steamtown USA founder Nelson Blount created the non-profit Steamtown Foundation for the Preservation of Steam and Railroad Americana to take over Steamtown USA and his train collection so that Union Pacific would donate the engine.
Union Pacific “Big Boy” No. 4012 on display at Steamtown National Historic Site
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Last updated on March 5, 2024
