The World's Biggest Steam Locomotive Sat Idle for 51 Years

Union Pacific's Big Boy No. 4014 is the largest steam locomotive running anywhere on Earth today. For 51 years it did not run at all. It sat parked at a county fairground in Pomona, California, as a static museum piece, until Union Pacific hauled it home and turned it back into a working machine.

1.2 Million Pounds of Steel

The American Locomotive Company built No. 4014 in Schenectady, New York, in 1941. Union Pacific ordered the class to haul heavy freight trains over the Wasatch Mountains between Wyoming and Utah without needing a second engine.

The finished locomotive stretches 133 feet from end to end and weighs 1.2 million pounds. Its frame is hinged in the middle so all that length can still bend around a curve. Fully loaded, it could produce more than 6,000 horsepower and pull loads no other steam engine of its era could handle alone.

Only One of Twenty-Five Still Runs

ALCO built 25 Big Boys between 1941 and 1944. Union Pacific ran No. 4014 for nearly two decades, logging just over a million miles, before retiring it from active service in 1959 and taking it off the roster in December 1961.

Today 8 of the 25 survive in museums and rail yards across the country. No. 4014 is the only one that still moves under its own steam.

Fifty-One Years as a Park Exhibit

Union Pacific donated No. 4014 to a local rail preservation society in December 1961. The locomotive arrived at what became the RailGiants Train Museum, on the Los Angeles County Fairgrounds in Pomona, on January 8, 1962.

It stayed there, cold and motionless, for the next 51 years. Generations of Southern California kids grew up visiting the giant black engine on school trips and weekend outings, never once seeing it move.

Union Pacific reacquired the locomotive in the summer of 2013. Movers spent months easing it across the fairgrounds parking lot before it finally left Pomona for good in January 2014, headed for Union Pacific's shops in Wyoming.

The Chalk Mark That Named It

Union Pacific's president wanted the new class named "Wasatch," after the mountain range it was built to conquer. During construction in 1941, an ALCO shop worker in Schenectady chalked two words on the smokebox of the first one instead: "Big Boy."

The name was never supposed to stick. It did anyway, and every one of the 25 locomotives has carried it ever since.

Bringing a Giant Back to Life

Union Pacific's Cheyenne shop crews spent years rebuilding No. 4014 piece by piece, converting it from coal to oil in the process. On the night of May 1, 2019, the locomotive moved under its own power for the first time in six decades.

The next day it made its first real run, from Cheyenne to Nunn, Colorado, officially becoming the largest operating steam locomotive in the world.

7,145 Miles for America's 250th

This spring and summer, No. 4014 made its first-ever coast-to-coast run, timed to celebrate America's 250th anniversary. It launched from Sacramento in April, toured the West first, then turned east from its Cheyenne home base in May.

By the time it rolled back into Cheyenne on July 29, 2026, it had crossed 14 states and covered 7,145 miles, making more than 75 whistle-stops. It was the first time Big Boy had steamed across the Mississippi River and into the Ohio Valley since it left the factory in 1941.

Over the Fourth of July weekend, thousands of people lined up at the Philadelphia Navy Yard just to stand next to it.

The engine that once sat frozen behind a fairgrounds fence for half a century is back home in Wyoming now, under steam, waiting for its next trip.