Under the Whyte notation for the classification of steam locomotive wheel arrangements, a 2-10-10-2 is a locomotive with two leading wheels, two sets of ten driving wheels, and a pair of trailing wheels.

Other equivalent classifications are:

UIC classification: 1EE1 (also known as German classification and Swiss classification)
Italian and French classification: 150+051
Turkish classification: 56+56
Swiss classification: 5/6+5/6

The equivalent UIC classification is refined to (1′E)E1′ for Mallet locomotives. All 2-10-10-2 locomotives have been articulated locomotives, Mallet locomotives in particular.

This wheel arrangement was rare. Only two classes of 2-10-10-2 locomotives have been built; the Atchison, Topeka and Santa Fe Railway's 3000 class, and the Virginian Railway's class AE. The Atchison, Topeka, and Santa Fe 3000 class unfortunately performed poorly, and therefore were rebuilt back to the original 2-10-2s they came from between 1915-1918, after only being in service for approximately 3-7 years. None of these survived into preservation. The Virginian Railway Class AE were much more successful, providing between 25-31 years of service, where some were scrapped from 1943-1945, and the rest were scrapped from 1947 to 1949 . None were preserved.

ATSF 3000 class[]

ATSF 3000 class
Detroit Publishing - New Mallet articulated compound engine on the Santa Fe (sky cropped).jpg
ATSF 3000 class 2-10-10-2. The forward section of the boiler is actually a primitive superheater and feedwater heater
Type and origin
Power typeSteam
Build date1911-1912
RebuilderBaldwin Locomotive Works and ATSF
Rebuild date1915-1918 (as 2-10-2’s)
Number rebuilt10
Driver dia.57 in (1.448 m)
Wheelbase108 ft 10 in (33.17 m)
Length122 ft (37.19 m)
Loco weight616,000 lb (279,400 kg; 279.4 t)
Tender weight266,400 lb (120,800 kg; 120.8 t)
Boiler pressure225 psi (1.55 MPa)
CylindersFour, compound, HP rear, LP front
High-pressure cylinder28 in × 32 in (711 mm × 813 mm)
Low-pressure cylinder38 in × 32 in (965 mm × 813 mm)
Performance figures
Tractive effort111,600 lbf (496 kN)
OperatorsAtchison, Topeka and Santa Fe Railway
DispositionAll scrapped

This class of ten 2-10-10-2 locomotives were actually rebuilt from more conventional 2-10-2 Baldwin-built locomotives by the Atchison, Topeka and Santa Fe Railway in 1911 to 1912.

Although they appeared to have exceedingly long boilers, the barrel in front of the rear set of cylinders actually contained first a primitive firetube superheater for further heating the steam before use; the steam was carried forward from the boiler proper by outside steam pipes as shown in the photograph. Also in this space was a reheater for the high-pressure exhaust before it was fed to the forward low-pressure cylinders.

In front of that, there was a feedwater heater, a space where cold water from the tender could be warmed before being injected into the water proper. This worked similarly to the boiler itself; the firetubes passed through the feedwater tank. The ATSF 2-10-10-2's, #3000 class locomotives, were the largest locomotives in the world from 1911 till possibly early 1914.

Despite being good for helper service, they could only go 10 to 15mph before losing steam, resulting in the locomotives being rebuilt to 2-10-2s during 1915–1918.

Virginian Railway class AE[]

Virginian Class AE
Virginian Railway AE.jpg
Virginian Class AE
Type and origin
Power typeSteam
BuilderAmerican Locomotive Company
Build date1918
Total produced10
 • Whyte2-10-10-2
Gauge4 ft 8 12 in (1,435 mm)
Driver dia.56 in (1,422 mm)
Wheelbase64.25 ft (19.58 m)
Width12.0 ft (3.658 m)
Height16.7 ft (5.090 m)
Adhesive weight617,000 lb (279,866 kg; 280 t)
Loco weight684,000 lb (310,257 kg; 310 t)
Tender weight231,000 lb (104,780 kg; 105 t)
Total weight915,000 lb (415,037 kg; 415 t)
Fuel typeCoal
Water cap13,000 US gal (10,825 imp gal; 49,210 L)
Tender cap.12 short tons (10.7 long tons; 10.9 t)
 • Firegrate area
109 sq ft (10 m2)
Boiler119 in (3,023 mm)
Boiler pressure215 psi (1 MPa)
Heating surface8,606 sq ft (800 m2)
 • Heating area2,120 sq ft (197 m2)
CylindersFour, compound, LP front, hp rear
High-pressure cylinder30 in × 32 in (762 mm × 813 mm)
Low-pressure cylinder48 in × 32 in (1,219 mm × 813 mm)
Loco brakeAir
Train brakesAir
Performance figures
Tractive effortCompound: 147,200 lbf (655 kN)
Simple: 175,000 lbf (778 kN)
Factor of adh.4.2
Number in class10
DispositionAll scrapped from 1943-1945,1947-1949

These ten locomotives were built in 1918 by ALCO for the Virginian Railway. Overall width was 144 inches (3,658 mm), so they were delivered without their cabs and the front, low-pressure cylinders and were assembled after arrival. The 48-inch (1,219 mm) low-pressure cylinders (on 90-inch or 2,286-millimetre centers) were the largest on any US locomotive; the cylinders had to be inclined a few degrees to provide clearance.[1] The boiler was also the largest diameter of any locomotive; Railway Mech Engnr says "the outside diameter of the largest course is 112 78 inches (2,867 mm)." but the drawing shows 118 12 inches (3,010 mm) diameter at the rear tube sheet.

As seen in the photograph, the tenders were small so they could use the Virginian's existing turntables.

This class were compound Mallet locomotives: as well as being articulated between the forward, swinging engine unit and the rear fixed one, they were compound locomotives. The rear, high-pressure cylinders exhausted their steam into the huge front cylinders. Like many compound locomotives, they could be operated in simple mode for starting; reduced-pressure steam could be sent straight from the boiler to the front cylinders at low speed, for maximum tractive effort.

Calculated in the usual way the tractive effort was 147,200 lb (66,800 kg) in compound; or 176,600 lb (80,100 kg) in simple for the Virginian locomotives.[2]

Unlike some other giant locomotives of the period, the immense boilers could generate enough steam to make them a success on the slow (8 mph or 13 km/h) coal trains for which they were built. They remained in service until the 1940s and could be called the ultimate drag era locomotive. No locomotive example of this type survived into preservation.[1]


  1. ^ a b c Bruce, Alfred. The Steam Locomotive in America: Its Development in the Twentieth Century. New York: W.W. Norton. pp. 321, photo 85.
  2. ^ Lewis, Lloyd D. (1993). Virginian Railway Locomotives (1 ed.). Marceline, Missouri: Walsworth Publishing Co. p. 32. ISBN 1-883089-05-0.

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