Union Pacific Big Boy steam locomotive, the largest operating steam locomotive in the world. This absolute unit is 26 meters long and weighs 600 tons when including its tender. It came around in 1941 after other locomotives were unable to pull trains up steep slopes in the Wasatch Mountains on their own, requiring help from other locomotives. The 4-8-8-4 Big Boy, with its tractive effort of 135,375 lbf, could do it alone. 25 were built in total, and they traveled millions of miles moving materials crucial to the war effort