BIG BOY 4014 in Nebraska, August 2019
Union Pacific Railroad's flagship legacy steam engine, one of only 8 survivors out of 25, and the only one restored to running condition, as of May, 2019.

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.

Eight Big Boys survive today, most on static display at museums across the country. One locomotive was re-acquired by the Union Pacific in 2013 to be restored to operating condition. The locomotive’s restoration was completed in May 2019 and made its first runs since 1959 that same month, allowing it to regain the title as the largest and most powerful operating steam locomotive in the world.

In May 2019, No. 4014 made its first excursion run amid the celebrations marking 150 years since the completion of the First Transcontinental Railroad. Following its May 4 christening at the Cheyenne Depot Museum, the locomotive — along with No. 844 — traveled to Ogden, Utah.

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