Which American railroad operated the Big Boy, among the largest steam locomotives ever built?

The Union Pacific Railroad operated the Big Boy, one of the largest and most powerful steam locomotive types ever built. The American Locomotive Company constructed 25 of these massive articulated 4-8-8-4 locomotives for Union Pacific between 1941 and 1944.

Big Boys were designed for heavy freight service over the Wasatch Range between Ogden, Utah, and Green River, Wyoming. Their four leading wheels, two groups of eight driving wheels, and four trailing wheels helped them handle curves while producing enormous tractive effort on mountain grades.

The locomotives were built during the Second World War, when freight traffic was surging. Later, they worked across parts of Wyoming, Utah, Colorado, and Nebraska. Rising costs and the spread of diesel-electric locomotives ended their regular service; the last revenue run took place in 1959, with a few units retained briefly afterward.

Eight Big Boys survive. Union Pacific restored No. 4014 to operating condition in 2019, making it the only operational Big Boy and a major attraction in the railroad’s heritage program.