On the Chesapeke & Ohio Railroad, as the number of cars grew on its passenger trains, it became necessary to doublehead "Pacifics" to get these longer trains over the Allegheny Mountains. In 1910, the C&O turned to the American Locomotive Company for a more powerful locomotive.

The engineers at ALCO made a study of the road conditions and other requirements . From this study they recomended a locomotive with eight drivers, like the "Mikado", for traction to which they would add a four-wheel lead truck, like the "Pacific", for speed and riding stability. The result was a new wheel arrangement, the 4-8-2.

The C&O agreed and, in 1911, became the first railroad to take delivery of a locomotive with the 4-8-2 wheel arrangement with the arrival of number 316 (this locomotive was later renumbered 540). The C&O named this new type of locomotive "Mountain" because it was developed to haul passenger trains over the Allegheny Mountains.

The "Mountain" 4-8-2 was a fast dual-service locomotive that was bought by many railroads in need of more motive power for the ever increasing weight of passenger trains and to compete for fast freight.

In North America 41 railroads bought or built 2,204 "Mountain" Locomotives. The New York Central and the Pennsylvania Railroad used a combined total of 901 or 41% of the total. The first one built was C&O number 316, in 1911, and the last one built was B&O number 5594, in 1948.

The 4-8-2 was the locomotive that demonstrated the value of combining eight coupled high drivers with the speed potential of the leading four wheel truck. Had the engineers, in 1911, recognized the serious limitation of the two trailing wheels and had allowed more weight by adding a trailing four wheel truck then the ultimate daul-service locomotive would have been developed 16 years earlier than the 1927 introduction of the "Northern".