# Big Boy 4014 (DD-720) > Big Boy No. 4014 is one of 25 4-8-8-4 'Big Boy' articulated steam locomotives that the American Locomotive Company (ALCO) built for Union Pacific. It was delivered in December 1941. Big Boys normally hauled freight between Ogden, Utah, and Cheyenne, Wyoming, across the Wasatch range. No. 4014 made its last revenue run in July 1959 and was retired in December 1961 after 1,031,205 miles. It was then displayed in Pomona, California, until Union Pacific reacquired it in 2013. After a restoration that included converting it from coal to oil, it returned to service in May 2019 and is now the world's largest operating steam locomotive. In 2026 it made a 14-state coast-to-coast America250 tour. - Department: History (also Tech) - First published: 2026-05-31 - Last updated: 2026-05-31 - Permalink: https://detailenjoyer.com/case/big-boy-4014/ - Author: Marcus Easterling (DetailEnjoyer), The Detail Department ## On the timeline - **December 1941**: Big Boy No. 4014 delivered to Union Pacific - **July 21, 1959**: No. 4014's final revenue run - **Dec. 7, 1961**: No. 4014 retired after 1,031,205 miles - **2013**: Union Pacific reacquires 4014 from Pomona - **May 2019**: 4014 returns to service - **April 10, 2026–July 29, 2026**: Coast-to-coast America250 tour Full timeline: https://detailenjoyer.com/timeline/?case=big-boy-4014 ## Quick facts - **DD-720-F01**: No. 4014 traveled 1,031,205 miles before retiring in 1961. _(Write-up · Exhibit C (Retirement))_ - **DD-720-F02**: It returned to service in May 2019 after Union Pacific converted it to burn oil. _(Write-up · Exhibit D (Restoration))_ ## Write-up Union Pacific's 1941 giant, back under steam. The only one of eight surviving Big Boys that still runs. 1. **Built for the Wasatch**: Union Pacific had 25 Big Boys built, the first delivered in 1941, to haul heavy wartime freight, usually between Ogden, Utah, and Cheyenne, Wyoming. No. 4014 was delivered in December 1941. 2. **Hinged giant**: At about 133 feet long and 1.2 million pounds, Big Boys have articulated, or hinged, frames to get around curves. The 4-8-8-4 arrangement means four pilot wheels, two sets of eight drivers, each driven by its own engine, and four trailing wheels. 3. **Retirement**: No. 4014 made its last revenue run on July 21, 1959, and was retired on December 7, 1961, after 1,031,205 miles. It was then displayed at the RailGiants Train Museum in Pomona, California. 4. **Restoration**: Union Pacific reacquired it in 2013 and moved it to its Steam Shop in Cheyenne. The restoration included converting it from coal to No. 5 fuel oil, and the locomotive returned to service in May 2019 for the 150th anniversary of the transcontinental railroad. 5. **Still touring**: Of the eight Big Boys that survive, 4014 is the only one that runs. In 2026, Union Pacific sent it on a 14-state coast-to-coast America250 tour, from Sacramento on April 10 to Cheyenne on July 29. ## Related case files - [Torque Conversion (DD-075)](https://detailenjoyer.com/case/torque-conversion/): Another case about how a machine delivers power - [Bethlehem Steel (DD-010)](https://detailenjoyer.com/case/bethlehem-steel/): Another case from American industrial history - [Knuckle Coupling (DD-303)](https://detailenjoyer.com/case/knuckle-coupling/): I paired it with another piece of North American railroading - [Earth Movers II (DD-639)](https://detailenjoyer.com/case/earth-movers-ii/): Another record-size machine ## Reel vs. record - **Precision**: it's the largest operating steam locomotive. Other Big Boys survive, but the other seven are static displays. - **Route**: Big Boys normally ran between Ogden, Utah, and Cheyenne, Wyoming, crossing the Wasatch range and the Wyoming plateau. - **Missing context**: the 4-8-8-4 is an articulated design with two engines, each with its own cylinders and eight drivers, under one boiler. The hinged frame lets it take curves. - **Missing context**: No. 4014 was retired in 1961, spent decades on display in Pomona, California, and returned to service in May 2019 after Union Pacific's restoration. - **Modern change**: the restored 4014 burns No. 5 fuel oil instead of coal. ## Video: Big Boy 4014: Union Pacific's 1941 Giant, Back Under Steam - Duration: 30.1 s · Published: 2026-05-31 - File: https://detailenjoyer.com/assets/videos/DZBlLN6RGYb.mp4 ### Transcript DID YOU KNOW? The Union Pacific Big Boy No.4014 is the largest operational steam locomotive in the world, and one of only 25 Big Boy locomotives ever built for the Union Pacific Railroad. Constructed in 1941 by the American Locomotive Company, it was designed to haul immense freight trains over the steep grades of the Wasatch Mountains between Utah and Wyoming. The locomotive measures more than 132 feet long, weighs over 1.2 million pounds with its tender, and uses a 4-8-8-4 wheel arrangement that effectively combines two sets of driving wheels under a single boiler. NOW YOU KNOW! ## Questions & answers **Q: How many Big Boys were built?** A: 25, all for Union Pacific. _(Source: Write-up · Exhibit A (Built for the Wasatch) · Union Pacific: Big Boy No. 4014; Union Pacific: Big Boy No. 4014 fact sheet (PDF))_ **Q: What's the Big Boy's wheel arrangement?** A: 4-8-8-4. _(Source: Write-up · Exhibit A (Built for the Wasatch) · Union Pacific: Big Boy No. 4014; Union Pacific: Big Boy No. 4014 fact sheet (PDF))_ **Q: When did 4014 return to service?** A: May 2019. _(Source: Write-up · Exhibit B (Hinged giant) · Union Pacific: Big Boy No. 4014)_ **Q: Where was 4014 displayed before its restoration?** A: RailGiants Train Museum, Pomona. _(Source: Write-up · Exhibit D (Restoration) · Union Pacific: Big Boy No. 4014; Wikipedia: Union Pacific 4014)_ **Q: What does the restored 4014 burn?** A: No. 5 fuel oil. _(Source: Write-up · Exhibit E (Still touring) · Union Pacific: Big Boy No. 4014 fact sheet (PDF); Union Pacific: Big Boy No. 4014 2026 Coast-to-Coast Tour)_ ## Sources - [Union Pacific: Big Boy No. 4014](https://www.up.com/about-us/history/steam/big-boy-4014) - [Union Pacific: Big Boy No. 4014 fact sheet (PDF)](https://www.up.com/content/dam/upcom/migration/uprr/newsinfo/documents/up-pdf-nativedocs/pdf-up-media-4014-fact-sheet.pdf) - [Wikipedia: Union Pacific 4014](https://en.wikipedia.org/wiki/UP_4014) - [Union Pacific: Big Boy No. 4014 2026 Coast-to-Coast Tour](https://www.up.com/about-us/history/steam/schedule/2026-coast-to-coast-tour) ## Cite this case file Easterling, Marcus. "Big Boy 4014." The Detail Department (DetailEnjoyer), case file DD-720, last updated May 31, 2026. https://detailenjoyer.com/case/big-boy-4014/