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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.

ATSF 3000 class[edit]

ATSF 3000 class 2-10-10-2. The forward section of the boiler is actually a primitive superheater and feedwater heater.

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.

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 experiment was unsuccessful and the locomotives were rebuilt to 2-10-2s during 1915–1918.


  • Road numbers: 3000–3009
  • Driver diameter: 57 in (1.4 m)
  • Weight: 616,000 lb (279,400 kg = 279.4 t)
  • tender weight 266,400 lb (120,8 t.)
  • total length 122 ft. (37,2 m)
  • overall wheelbase 108" 10' (32,95 m)
  • Tractive effort: 111,600 lbf (496 kN)
  • Boiler pressure: 225 psi (1.55 MPa)
  • Cylinder diameter: 28 in (710 mm) high pressure, 38 in (970 mm) low pressure
  • Cylinder stroke: 32 in (810 mm)

Virginian Railway class AE[edit]

Virginian Class AE
Virginian Railway AE.jpg
Virginian Class AE
Type and origin
Power type Steam
Builder American Locomotive Company
Build date 1918
Total produced 10
Configuration 2-10-10-2
Gauge 1,435 mm (4 ft 8 12 in)
Driver diameter 56 in (1,422 mm)
Wheelbase 64.25 ft (19.58 m)
Width 12.0 ft (4 m)
Height 16.7 ft (5 m)
Weight on drivers 617,000 lb (280 t)
Locomotive weight 684,000 lb (310 t)
Tender weight 231,000 lb (105 t)
Locomotive and tender
combined weight
915,000 lb (415 t)
Fuel type Coal
Water capacity 13,000 US gal (49,210 l)
Tender capacity 12 tons (11 t)
Boiler 119 in (3,023 mm)
Boiler pressure 215 psi (1 MPa)
Firegrate area 109 sq ft (10 m2)
Heating surface:
– Total
8,606 sq ft (800 m2)
Superheater area 2,120 sq ft (197 m2)
Cylinders 4
Front cylinder
48 in × 32 in (1,219 mm × 813 mm)
Rear cylinder
30 in × 32 in (762 mm × 813 mm)
Performance figures
Tractive effort Compound: 147,200 lbf (655 kN)
Simple: 175,000 lbf (778 kN)
Factor of
Locomotive brake Air
Train brakes Air
Operator(s) Virginian
Number in class 10
Number(s) 800-809
Disposition All scrapped

These ten locomotives were built in 1918 by ALCO for the Virginian Railway. Overall width was 144 inches, so they were delivered without their cabs and the front, low pressure cylinders and were assembled after arrival. The 48-inch low pressure cylinders (on 90-inch 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 7/8 in." but the drawing shows 118-1/2 inches 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 (assuming equal tractive effort from the two engines and mean effective pressure adding up to 0.85 times boiler pressure) the tractive effort was 135,200 lb in compound; in the US, compound Mallets were credited with 20% more tractive effort in simple mode, or 162,200 lb for the Virginian locomotives.

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.[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.