When railfans think of "big steam," one locomotive almost always comes to mind: the Big Boy.

The World's Most Famous Steam Locomotive

Often regarded as the largest steam locomotive ever built - and certainly a contender for the world's most famous locomotive - the Big Boy was created to meet some of the most demanding operating requirements ever placed on a steam engine. The Union Pacific Railroad needed a locomotive capable of hauling a 3,600-ton train over Sherman Hill and the 1.14% grade between Ogden and Wasatch, Utah, without the assistance of helper locomotives.

When the final design specifications were completed, Union Pacific and ALCO settled on a simple articulated locomotive built for both power and speed. Measuring 132 feet in length and riding on sixteen 68-inch drivers, the resulting 4-8-8-4 was among the longest, heaviest, and most powerful steam locomotives ever constructed. Legend has it th