1. Home
 ›
2. Steam Locomotives
 ›
3. 2-6-6-6

2-6-6-6 "Allegheny" Locomotives: Length, Horsepower, Specs

Last revised: February 27, 2025

By: Adam Burns

The Allegheny is widely regarded as the most powerful steam locomotive ever built in terms of drawbar horsepower (dbhp).  

The articulated design was of the 2-6-6-6 wheel arrangement and based purely on horsepower and tractive effort nothing could top it.  The engine's boiler could produce an incredible 8,000 horsepower while dbhp, according to Walter Simpson's "The Steam Locomotive Energy Story," was rated at between 7,000-7,498 (depending on the source).

The locomotive's name was derived from the territory it served, the Allegheny Mountains of western Virginia/southeastern West Virginia.  Ultimately, Lima produced 60 Alleghenies for C&O between 1941-1948 while the nearby Virginian would acquire 8 examples of similar design.

Despite their formidable strength and endurance, their reign was short-lived. The advancement of diesel-electric technology signaled the end of steam production in America.  By 1956, all Alleghenies had been retired while Virginian's eight Blue Ridge examples were scrapped by 1960.

Today, two survive, both of C&O heritage: #1604 at the Baltimore & Ohio Railroad Museum and #1601 at the Henry Ford Museum. The latter engine has been very well-preserved, having remained indoors since its retirement.  In fact, it is said to occasionally still leak oil!

Photos

Chesapeake & Ohio 2-6-6-6 #1624 hustles train #95 around a curve west of Deep Water, West Virginia on June 6, 1956. Bill Price photo. American-Rails.com collection.

Overview

The C&O remained a strong proponent of steam through the 1940s due, in part, to its considerable coal business which offered a cheap and abundant source of fuel.

As freight continued to grow following the lean years of the 1930s, the railroad was interested in more powerful locomotives to augment its fleet of 2-10-4s as well as more easily handle the stiff grades of its Hinton-Clifton Forge main line. This particular territory featured grades ranging between 0.58% and 1.14%.

Virginian Railway 2-6-6-6 #903 (AG) is seen here at Roanoke, Virginia during the NRHS's 1957 annual convention. The railroad had several of its now-famous locomotives on display, including its EL-C and EL-2B electrics (both visible in the background). Fred Byerly photo. American-Rails.com collection.

Chesapeake & Ohio

At the time of the Allegheny's development the railroad was using powerful, but somewhat older wheel arrangements, including its reliable T-1 2-10-4s as well as larger 2-6-6-2s and 2-8-8-2s.

Interestingly, when the railroad set out to build a more powerful engine - via recommendation of its Advisory Mechanical Committee (AMC) - the goal was not to outperform Union Pacific's then-in-development "Big Boy."  Instead, the hope was to outclass Norfolk & Western's home-built 2-6-6-4s.

In his book, "The American Staem Locomotive In The Twentieth Century," author Tom Morrison notes the Allegheny's development was not solely the work of the Lima Locomotive Works. 

The C&O's own AMC is largely responsible for the design, which wanted a locomotive that could not only tackle the Hinton-Clifton Forge grades but also handle freights between Russell, Kentucky and Toledo, Ohio at 30-35 mph.

The C&O studied the Seaboard Air Line's 2-6-6-4s and UP's 4-6-6-4 in planning the new articulated design.  It was decided the locomotive should not only be powerful but also capable of operating at high speeds.  The latter stipulation proved quite ironic considering the 2-6-6-6s were rarely ever utilized in such service.

Horsepower

In tests, the new wheel arrangement was capable of producing a stunning 7,498 drawbar horsepower (dbhp), nearly 1,200 more than either the Big Boy (6,300) or N&W's Class As (6,300).

Genrally, the locomotive could produce a continous drawbar horsepower output of between 6,700-6,900 at 42-46 mph.  As Mr. Morrison notes, a 2-6-6-6 could accelerate 160 loads - weighing 14,100 tons - from a standstill to 19 mph in a single mile.  In addition, it could reach 29 mph in just 11 minutes. 

The Alleghenies proved one of the heaviest reciprocating steamers ever built, weighing 751,830 pounds.  By comparison, Norfolk & Western's 2-6-6-4's weighed 573,000 pounds and the 4-8-8-4's 772,250 pounds.  With its tender, an Allegheny weighed 1,183,540 pounds.

Mr. Morrison's book goes on to note the following:

"The trailing truck supported a partly welded firebox containing 135 square feet of Firebar grates with 25% air opening and three siphons with a combustion chamber extending 9 feet 10 inches ahead of the throat sheet.

The 6-wheel trailing truck alone, with cast-steel frame and brakes, weighed 43,000 pounds.  The water legs were generously sized at 7 inches. A 14,500-gallon per hour injector and a 14,000-gallon per hour Worthington feedwater heater supplied the boiler.

The total crown sheet length of 27 feet exceeded the 23-foot length of the tubes, providing 7,240 square feet of evaporative surface and 3,185 square feet in the Type E superheater (probably the biggest heating surface ever built into a steam locomotive) and generating steam at 260 psi.

Baker valve gear and 12-inch piston valves suppled steam to four 22 ½-inch x 33-inch cylinders driving 67-inch Boxpok driving wheels for a tractive effort of 110,000 pounds.  The engine weighed 725,000 pounds with a very high axle loading of 79,000 pounds."

A big Virginian Railway 2-6-6-6, #903 (Class AG), is seen here in Norfolk, Virginia during December of 1954. American-Rails.com collection.

In designing the locomotive, Lima and Chessie had to keep the engine's length within the bounds of C&O's turntables.  The solution was to incorporate angling into the tender, which was larger at the rear.

The design increased capacity while reducing the engine's overall length, which was still an impressive 113 feet. This resulted in an uneven truck setup, four axles at the rear and three in front with a capacity of 25,000 gallons (water) and 25 tons of fuel (coal).

With its 67-inch drivers and 110,000 pounds of tractive effort, an Allegheny could move 5,000 tons of freight at an incredible 45 mph.  Curiously, as SteamLocomotive.com notes, Chessie often employed them in drag service lugging 10,000 ton freights at 15 mph.  Interestingly, 23 of the engines were even equipped with steam heat and signal lines for passenger service but were rarely ever used in this capacity.

Chesapeake & Ohio 2-6-6-6 #1606 (H-8) was photographed here by Bill Price at the terminal in Handley, West Virginia, circa 1951. American-Rails.com collection.

The C&O's decision not to use the engines as intended made Ed King wonder in his article "Big Boy Or Big Mistake?" from the September, 2004 issue of Trains magazine, if the Alleghenies were really ever worth the investment.

The railroad's 60 engines had cost $230,000 each, nearly twice the cost of the Norfolk & Western's Class As, which had been built at the Roanoke Shops for $123,000 a piece.  Given how they were used, King points out that a Class H-7 2-8-8-2 from the 1920s had a tonnage rating of just 200 less than an Allegheny.

Specifications

The Big Boys may have garnered more publicity but the 2-6-6-6s were more powerful and are often credited as the pinnacle of "Super Power" steam technology.  Sadly, these locomotives were practically new when retired; the oldest barely ten years of age before the C&O began retiring the fleet in 1952.  

Chesapeake & Ohio 2-6-6-6 #1632 hustles eastbound loads of coal over the main line in eastern Kentucky, circa 1952. In the background is the mighty Ohio River. American-Rails.com collection.

Virginian Railway

Chessie was not the only buyer of the 2-6-6-6. The Virginian also purchased eight of its own in 1945, numbered 900-907, which named them the Blue Ridge.  The railroad likely would never have purchased the locomotives had it not been for president Frank Beale, who came to the Virginian from the C&O.

During his time at the Chessie, Beale worked as a senior manager through the Allegheny territory where the 2-6-6-6s first entered service and was impressed with the articulateds, deciding the Virginian needed its own fleet.

The railroad's stiff grades precluded its 2-6-6-6s from being used in high-speed service as intended and they normally did not operate faster than 35 mph. After only 15 years of service these massive locomotives were also scrapped in 1960.

The Allegheny embodied perfection and power in steam era technology.  The design, continues to inspire admiration and respect for its technical achievements, symbolising both the zenith of steam locomotive development and its inevitable end.

The locomotive's story is etched into the annals of railroad history, bearing witness to the glory and majesty of the rail empire in its prime, marked by an extraordinary blend of human ingenuity and mechanical prowess. This iron beast is an enduring emblem of a bygone era, forever encapsulating the allure and romance of steam.

Sources

• Dixon, Thomas W. Chesapeake And Ohio Railway:  A Concise History And Fact Book.  Clifton Forge:  Chesapeake & Ohio Historical Society, 2012.

• Lewis, Lloyd D.  West Virginia Railroads Volume 4:  Virginian Railway.  Forest:  TLC Publishing, Inc., 2011.

• Morrison, Tom. American Steam Locomotive In The Twentieth Century. Jefferson: McFarland & Company, Inc., 2019.

• Simpson, Walter. Steam Locomotive Energy Story, The.  New York: American University Presses, 2021.