Diagram of one small leading wheel and two trios of large driving wheels, each trio joined by a coupling rod
Front of locomotive at left
Class MA 2-6-6-0 no. 336.jpg
Equivalent classifications
UIC class(1C)C, (1'C)C
French class130+030
Turkish class34+33
Swiss class3/4+3/3
Russian class1-3-0+0-3-0
First known tank engine version
First use1906
CountryNew Zealand
LocomotiveNZR E class Pearson's Dream
RailwayNew Zealand Railways
DesignerG.A. Pearson
BuilderNZR Petone Workshops
First known tender engine version
First use1909
CountryColony of Natal
LocomotiveNGR 2-6-6-0, SAR Class MA
RailwayNatal Government Railways
DesignerAmerican Locomotive Company
BuilderAmerican Locomotive Company

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 2-6-6-0 is a locomotive with one pair of unpowered leading wheels, followed by two sets of three pairs of powered driving wheels and no trailing wheels. The wheel arrangement was principally used on Mallet-type articulated locomotives. Some tank locomotive examples were also built, for which various suffixes to indicate the type of tank would be added to the wheel arrangement, for example 2-6-6-0T for an engine with side-tanks.


The 2-6-6-0 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]


New Zealand[]

The sole NZR E class locomotive of 1906 was the only 2-6-6-0T locomotive ever built for and used by the New Zealand Railways Department. It was built at the Petone Workshops in Wellington and was designed for use on the world famous Rimutaka Incline. Numbered 66, making it E 66, it spent the first part of its working life in the Wellington region hauling trains up and down the Rimutaka Incline. It was eventually transferred to the Wellington-Johnsonville section for banking duties, even though it was not designed for that type of work. In 1917, E 66 was withdrawn from service and scrapped. Sadly, it didn't survive long enough for preservation.[4]

South Africa[]

The South African Railways (SAR) operated 57 Mallet locomotives with this wheel arrangement, spread over six classes, all of them 3 ft 6 in (1,067 mm) Cape gauge.

United States of America[]

Virginian Railway Class AA Mallet

At least two American railroads used 2-6-6-0 Mallet locomotives. One was the Denver, Northwestern and Pacific Railway, which later became the Denver and Salt Lake Railroad and eventually the Denver and Salt Lake Railway. Towards the end of their service life, after the acquisition of the Denver and Salt Lake, these locomotives were used by the Denver and Rio Grande Western Railroad (D&RGW). The locomotives were initially used across the Rollins Pass and later on the Moffat Tunnel route of the Denver and Salt Lake. They were all scrapped by the D&RGW between 1948 and 1952. None were preserved.

Another was the Virginian Railway, whose Class AA 2-6-6-0 is depicted.


  1. ^ Compounding Steam Engines
  2. ^ a b Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 103–105. ISBN 978-0-7153-5382-0.
  3. ^ a b c d e f g Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 84–85, 87–88. ISBN 0869772112.
  4. ^ E. J. McClare, Steam Locomotives of New Zealand, Part Two: 1900 to 1930 (Wellington: New Zealand Railway and Locomotive Society, 1988), 95.
  5. ^ a b c d e f Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 13–14, 21–22, 29, 36–37, 140. ISBN 978-0-7153-5427-8.
  6. ^ a b c Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer’s Office, Pretoria, January 1912, pp. 9, 12, 15, 46 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
  7. ^ a b c North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
  8. ^ a b South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  9. ^ Hendrie (10 December 1921). "Engine Power on the S.A.R." South African Mining and Engineering Journal. XXXII (1576): 529.
  10. ^ North British Locomotive Co. works list (from J. Lambert)
  11. ^ Durrant, A. E. (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 24–25. ISBN 0715386387.