Virginian Railway Class AC No. 517.

(See page for author, Public domain, via Wikimedia Commons)



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.


The 2-6-6-0 Wheel Arrangement. Front of locomotive on left.

(By Gwernol - Own work, Public Domain,


Useage in the United States

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. None were preserved; they were all scrapped by the D&RGW between 1948 and 1952.

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


Virginian Railway Class AA Mallet.

(See page for author, Public domain, via Wikimedia Commons)



Equivalent classifications

  • UIC class (1C)C, (1'C)C
  • French class 130+030
  • Turkish class 34+33
  • Swiss class 3/4+3/3
  • Russian class 1-3-0+0-3-0

First known tank engine version
First use: 1904
Country: Dutch East Indies (Indonesia)
Locomotive: SS Class 520 (DKA CC10)
Railway: Staatsspoorwegen
Designer: Sachsische Maschinenfabrik (Hartmann)
Builder: Sachsische Maschinenfabrik
First known tender engine version
First use: 1909
Country: Colony of Natal
Locomotive: NGR 2-6-6-0, SAR Class MA
Railway: Natal Government Railways
Designer: American Locomotive Company
Builder: American Locomotive Company