Diagram of one small leading wheel, two trios of large driving wheels with each trio joined by a coupling rod, and one small trailing wheel
MD Mallett 1001.jpg
Equivalent classifications
UIC class(1C)C1, (1'C)C1'
French class130+031
Turkish class34+34
Swiss class3/4+3/4
Russian class1-3-0+0-3-1
First known tender engine version
First use1910
CountrySouth Africa
LocomotiveSAR Class MD
RailwayCentral South African Railways
DesignerAmerican Locomotive Company
BuilderAmerican Locomotive Company

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 2-6-6-2 is a locomotive with one pair of unpowered leading wheels, followed by two sets of three pairs of powered driving wheels and one pair of trailing wheels. The wheel arrangement was principally used on Mallet-type articulated locomotives, although some tank locomotive examples were also built. A Garratt type locomotive with the same wheel arrangement is designated 2-6-0+0-6-2.

Under the UIC classification the wheel arrangement is referred to as (1'C)C1' for Mallet locomotives.


The 2-6-6-2 wheel arrangement was most often used for articulated compound steam Mallet locomotives. In a compound Mallet, the rear set of coupled wheels are driven by the smaller high pressure cylinders, from which spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.[1][2][3]

This type of locomotive was commonly used in North America on logging railroads. The 2-6-6-2 wheel arrangement was also used in South Africa and the Soviet Union.



Serbian narrow gauge 2-6-6-2 compound Mallet

The Serbian government used a Mallet articulated compound locomotive for freight service on 2 ft 6 in (762 mm) narrow gauge. It was built for the Serbian government by the American Locomotive Company (ALCO).

South Africa[]

The South African Railways (SAR) operated 22 Mallet locomotives with this wheel arrangement, spread over five classes, all of them built to 3 ft 6 in (1,067 mm) Cape gauge.

CSAR no. 1023, SAR Class MF

Soviet Union[]

The wheel arrangement also appeared in Soviet Russia as a 5 ft (1,524 mm) locomotive, the P34, built by Kolomna Locomotive Works. It was a modern but compact Mallet of which only one was built.

United States[]

This "Mallet Mogul" wheel configuration existed on both the Norfolk & Western Railroad as Class L-76 (built by Norfolk & Western), later sold to Denver and Rio Grande Western, and the Denver and Rio Grande Western's standard gauge line as Class 340/L-62 (built by Alco-Schenectady), and in 1947 the Class L-76 from Norfolk & Western. D&RGW purchased these for helper service in 1910 (Soldier Pass and Tennessee Pass), and later added the two N&W locomotives to "beef up helper helper service" once again. All were retired between 1947-1952.


  1. ^ Compounding Steam Engines
  2. ^ a b c d Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 54–56, 103–105, 138–140. ISBN 978-0-7153-5382-0.
  3. ^ a b c d e f Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 86–87. ISBN 0869772112.
  4. ^ a b c d e Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 16–19, 30–32, 140. ISBN 978-0-7153-5427-8.
  5. ^ a b c d Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer’s Office, Pretoria, January 1912, pp. 9, 12, 15-16, 46-47 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
  6. ^ a b North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser