2-6-6-6 "Allegheny" Locomotives in the USA

An Allegheny Locomotive

What were the most powerful steam locomotives ever built? The Big Boys? Nope. What was the heaviest steam locomotive ever built? The Big Boys? Well, maybe, maybe not. Read on to find out the answer.

The Chesapeake & Ohio and the Virginian were the only two railroads to have this type of locomotive. The C&O called them Alleghenies. The Virginian called them the Blue Ridge type.

Number of "Allegheny" Type Locomotives Built by Year
Year
Railroad19411942194319441945194619471948Totals
Road Numbers1600-16091610-16191620-1644900-9071645-1659
C&O1010 25 1560
VGN 8 8
Totals:10102581568

A Dimensional Comparison of Large Locomotives

Books and magazines will often state that the Big Boy was the largest steam locomotive ever built. But, what do they mean by "largest"? When comparing steam locomotives, many different quantities can be considered. For example, weight, length, horsepower, and tractive effort are all characteristics of how "large" a steam locomotive is. In many of these categories, a locomotive "larger" than a Big Boy can be found. Does this mean that all of those books and magazines are wrong?

If you were to ignore all of the unsuccessful and experimental locomotives, then look at the overall ratings of the remaining steam locomotives in the above categories, it would become clear that there were many large locomotives. One could argue that the Big Boys were the largest and maybe they were. But the NP Z-5, the DM&IR M-3/4, the C&O H-8, and the N&W Y6b were all examples of the largest of all successful steam locomotives.

RailroadNPSPDM&IRB&OUPWPSPUPC&ON&WN&WPRRPRR
ClassZ-5AC-9M-3/M-4EM-1Big Boy (4884-2)M-137AC-10/11/124664-5H-8 - 1645Y6bAQ2S1
Wheel Arrangement2-8-8-42-8-8-42-8-8-42-8-8-44-8-8-42-8-8-24-8-8-24-6-6-42-6-6-62-8-8-22-6-6-44-4-6-46-4-4-6
Series5001-50113800-3811220-2377600-76294020-4024251-2604205-42943930-39491645-16592171-22001200-12426175+6100
Cyl:Dia x Stroke26x3224x3226x3224x3223.75x3226x3224x3221x3222.5x3325x3224x3019.75x2822x26
Driver Diameter6363.56364686363.5696758706984
Boiler Pressure250250240235300235250280260300300300300
Grate Area182139.5125117.5150145139132135106.2122121.7132
Evaporative Heating Surface7,6736,9186,7825,2985,7556,8116,4704,6426,7954,9156,6396,7255,661
Superheater Heating Surface3,2192,8312,7702,1182,0432,1522,6161,7412,9221,4782,7032,9302,085
Weight on Drivers558,900531,200560,257485,000545,200552,700531,700404,200504,010548,500432,350393,000281,450
Total Engine Weight723,400689,900695,040628,700772,250665,100657,900634,500751,830611,520573,000619,100608,170
Maximum Axle Weight70,90066,40062,10067,80069,08869,10085,48072,00079,780
Tender Weight402,000400,700438,000382,000436,500408,250393,300434,500431,710378,600378,600422,000451,840
Total Engine and Tender Weight1,125,4001,090,6001,133,0401,010,7001,208,7501,073,3501,051,2001,069,0001,183,540990,120951,6001,041,1001,060,010
Overall Wheelbase110.08112.99113.49112.5117.58108112.17106.67112.92114.87108.27107.62123.76
Tractive Effort145,930123,364140,093115,056135,375137,174123,36497,352110,211124,644125,897100,81676,403
Tractive Effort Booster13,40013,90015,000
Maximum Speed80636050100
Drawbar Horsepower6,345@41.56,000@407,498@465,600@255,300@437,200

Railroads that used 2-6-6-6 "Allegheny" Locomotives in the USA (data provided by Steve Llanso of Sweat House Media)

Surviving Examples of 2-6-6-6 "Allegheny" Locomotives in the USA

No.ClassF.M. WhyteGaugeRailroad LineLocationStatusBuilder InfoNotes
1604H-82-6-6-64'-8½"C&O B&O Railroad Museum, Baltimore, MDdisplayLima #7824, 1941From Russell, KY the Roanoke, VA
1601H-82-6-6-64'-8½"C&O Henry Ford Museum, Dearborn, MIdisplayLima #7821, 1941

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