The Union Pacific Big Boy is a steam locomotive built by the American Locomotive Company, with greater tractive effort and horsepower. They are the only locomotives to have the 4-8-8-4 wheel arrangement suitable for stability entering curves, and support for the firebox. It can generate a maximum of 6,290 drawbar horsepower. The picture features the 4004 Big Boy. The well-planned design of the locomotive predicts its efficiency successfully.