Table abuse FTW.

Talk about a disgusting amount of power. The H-8 Alleghenies certainly fall into (and essentially lead) this category of locomotive with their 7,500 horsepower. Keep in mind that the largest steam locomotive ever built, the Union Pacific Big Boy, created about 6200 horsepower. Only one steam locomotive surpassed the H-8 in overall horsepower (The Pennsylvania's Q-2 Class).

The H-8’s are a product of the Chesapeake & Ohio’s requirement for an updated heavy hauler for coal drags through, fittingly enough, the Allegheny mountains where the C&O’s main coal customers were located. The line in question ran from Hinton, West Virginia to Clifton Forge, Virginia and hosted a heavy grade and a steep summit that posed a challenge for material hauling. The C&O, like many East Coast railroads at this time, depended on coal traffic as a major source of income during a time when coal was king and World War II was looming. Slews of coal trains had to be transported to sorting points both east and west of the mountains. You could say that nearly every railroad had their own heavy hauler and throughout much of steam era, were constantly trying to find ways to improve on their designs.

The biggest locomotives in use by the C&O during the late 1930s were Mallet-type articulated locomotives such as 2-6-6-2s which were becoming outdated, as they were introduced in the early 20th century. While the C&O had already ordered a batch of new “Texas” type 2-10-4 locomotives to replace these engines (and was looking to buy more), the Lima Locomotive Works saw the railroad’s need for a more capable locomotive with still more horsepower and had a design in the works. The C&O was obviously interested and starting in 1941, the C&O agreed to start making purchases.

What Lima had was the H-8 Class. The H-8 “Allegheny” was a locomotive that was, simply put, gigantic for its day. The locomotive had four 22 ½” diameter cylinders, a 260 PSI boiler and 67” driving wheels. The firebox of the locomotive was so large that a traditional two or four-truck trailing wheel set was not suitable, and a six-truck set was used. The tender of the locomotive was designed to be big enough to feed the engine’s appetite for fuel (holding 25 tons of coal and 25,000 gallons of water) yet was built small enough to allow the locomotive to fit on C&O’s turntables in use at the time.

The Alleghenies backed up their impressive size with the ability to pull 5000 tons at about 50 MPH. However, the H-8’s got most of their work done hauling 10,000-ton trains at much slower speeds. Two H-8’s could haul almost 150 loaded hoppers at around 20 MPH. While known to have achieved 7500 horsepower, the H-8’s could consistently produce about 6800 horsepower, which was more than enough for the C&O. From a modern standpoint, the world’s most powerful diesel locomotive currently (General Electric’s AC6000CW) produces roughly 6200 horsepower.

It is believed that the C&O never really utilized the H-8’s to their truest potential like the Union Pacific did their Big Boys; hauling long trains at high speeds. The Alleghenies could have been the ultimate freighter in these terms. Instead, they were delegated to heavy freight hauling, which they did very well. The Alleghenies were all out of service by the late 1950s and replaced as multiple-unit diesel operation, which was easier on railroad track and was more practical and economical, overshadowed single-unit steam locomotives.

EDIT: Added a new picture of the 2-10-4. One that is actually a 2-10-4.