A hand-colored photo postcard of a Santa Fe Railway 2-10-10-2 locomotive being demonstrated in Emporia, Kansas in 1912.

(Fred Harvey, Public domain, via Wikimedia Commons)


Alco logo
Baldwin logo.


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 of the Mallet type.


A diagram of the 2-10-10-2 wheel arrangement. Front of locomotive is at left.

(Gwernol, Public domain, via Wikimedia Commons)


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 3000 class performed poorly, so the railroad returned them to their original 2-10-2 configuration after no more than seven years of service. None survive today. The class AE locomotives were much more successful, providing between 25 and 31 years of service; some were scrapped between 1943 and 1945, and the rest were scrapped between 1947 and 1949. None were preserved.


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

(Detroit Publishing Co. , publisher, Public domain, via Wikimedia Commons)


ATSF 3000 class

In 1911 and 1912, the Atchison, Topeka and Santa Fe Railway modified ten 2-10-2 Baldwin-built locomotives into a new 2-10-10-2 configuration dubbed the 3000 class. They were the largest locomotives in the world from their introduction until 1914. They performed well in helper service, but could only go 10 to 15 mph (16 to 24 km/h) before losing steam. The ATSF returned them to their 2-10-2 configurations between 1915 and 1918.


Atchison Topeka & Sante Fe Railroad engine 3003, a mallet locomotive on the tracks outside Winslow, Arizona in 1913-14.

(Harold Bartle Phelps Sr., Public domain, via Wikimedia Commons)


The first 2-10-10-2s were constructed in 1911 by the Atchison, Topeka and Santa Fe Railroad at a cost of $43,880 each. They were built out of existing 900 & 1600 class 2-10-2s with new front engines and tenders from Baldwin. They were used between Bakersfield and Barstow and up to San Bernardino. The railroad built 10 of these engines, which were cobbled together by the Santa Fe using existing 2-10-2 engine units united with low-pressure engine units supplied by Baldwin. Baldwin also designed and built the unusual "turtleback" tender that probably was designed to improve rearward vision.

A distinctive ribbed firebox trailed the long boiler. Like other Santa Fe Mallets, the actual tube length was relatively short, but a "reheater" ahead of the forward tube sheet and boiler joint was supposed to maintain steam heat as it traveled forward to the high-pressure cylinders. It added 2,659 sq ft, but was nowhere nearly as efficient as later superheater designs. The design was unsuccessful and the engines were converted back to 2-10-2 simple-expansion locomotives in 1915-1918.


ATSF 3000 class Overview

Type and origin
Power type: Steam
Builder: Baldwin Locomotive Works
Build date: 1911-1912
Rebuilder: ATSF
Rebuild date: 1915-1918 (as 2-10-2’s)
Number rebuilt: 10
Driver diameter:  57 in (1.448 m)
Wheelbase: 108 ft 10 in (33.17 m)
Length: 122 ft (37.19 m)
Locomotive weight: 616,000 lb (279,400 kg; 279.4 t)
Tender weight: 266,400 lb (120,800 kg; 120.8 t)
Total weight: 882,400 lb (400,180 kg; 400.18 t)
Boiler pressure: 225 psi (1.55 MPa)
Cylinders: Four, compound, HP rear, LP front
High-pressure cylinder: 28 in × 32 in (711 mm × 813 mm)
Low-pressure cylinder: 38 in × 32 in (965 mm × 813 mm)
Performance figures
Tractive effort: 111,600 lbf (496 kN)
Operator: Atchison, Topeka and Santa Fe Railway
Road Numbers: 3000–3009
Withdrawn: 1945-1953
Scrapped: 1947-1953
Disposition: All scrapped


Virginian Class AE 2-10-10-2 No. 802 builders photo, 1911.

(Morven, Public domain, via Wikimedia Commons)


Virginian Railway class AE

These ten locomotives were built in 1918 by ALCO for the Virginian Railway. With a width of 144 inches (3,658 mm), they were delivered without their cabs and front low-pressure cylinders; and were assembled after delivery. The 48-inch (1,219 mm) low-pressure cylinders (on 90-inch or 2,286-mm centers) were the largest on any U.S. locomotive; the cylinders had to be inclined a few degrees to provide clearance. The boiler was also the largest diameter of any locomotive; Railway Mechanical Engineer stated "the outside diameter of the largest course is 112+7⁄8 inches (2,867 mm)", but the drawing shows 118+1⁄2 inches (3,010 mm) diameter at the rear tube sheet. Their accompanying fuel tenders were shorter than usual so the locomotive would fit on the Virginian's turntables.

This class were compound Mallet locomotives. The rear, high-pressure cylinders exhausted their steam into the huge front cylinders. They could also 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.

The calculated tractive effort was 147,200 lb (66,800 kg) in compound; or 176,600 lb (80,100 kg) in simple for the Virginian locomotives.

The class remained in service until the 1940s. No locomotive example of this type survived into preservation.


Virginian Class AE Overview

Type and origin
Power type: Steam
Builder: American Locomotive Company
Build date: 1918
Total produced: 10
​• Whyte 2-10-10-2
Gauge: 4 ft 8+1⁄2 in (1,435 mm)
Driver diameter: 56 in (1,422 mm)
Wheelbase: 64.25 ft (19.58 m)
Width: 12.0 ft (3.658 m)
Height: 16.7 ft (5.090 m)
Adhesive weight: 617,000 lb (279,866 kg; 280 t)
Locomotive weight: 684,000 lb (310,257 kg; 310 t)
Tender weight: 231,000 lb (104,780 kg; 105 t)
Total weight: 915,000 lb (415,037 kg; 415 t)
Fuel type: Coal
Water cap. 13,000 US gal (10,825 imp gal; 49,210 L)
Tender capacity: 12 tons (10.7 long tons; 10.9 t)
• Firegrate area: 109 sq ft (10 m2)
Boiler: 119 in (3,023 mm)
Boiler pressure: 215 psi (1 MPa)
Heating surface: 8,606 sq ft (800 m2)
​• Heating area: 2,120 sq ft (197 m2)
Cylinders: Four, compound, LP front, hp rear
High-pressure cylinder: 30 in × 32 in (762 mm × 813 mm)
Low-pressure cylinder: 48 in × 32 in (1,219 mm × 813 mm)
Valve gear: Walschaerts
Locomotive brake: Air
Train brakes: Air
Performance figures
Tractive effort: Compound: 147,200 lbf (655 kN)
Tractive effort: Simple: 176,600 lbf (786 kN)
Factor of adhesion: 4.2
Operator: Virginian
Number in class: 10
Road Numbers: 800-809
Disposition: All scrapped from 1943-1945,1947-1949