Black Hills Central Baldwin Mallet No. 110 a 2-6-6-2T, June 4th 2013.

(Drew Jacksich from San Jose, CA, California Republic, CC BY 2.0 <>, via Wikimedia Commons)



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 locomotive or Golwé locomotive with the same wheel arrangement is designated 2-6-0+0-6-2 since both engine units are pivoting.

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


Schematic of 2-6-6-2 steam locomotive wheel arrangement.

(Gwernol, Public domain, via Wikimedia Commons)



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.

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.


Chesapeake and Ohio 2-6-6-2 No. 1309 on the Western Maryland Scenic Railroad.

(Fan Railer, CC BY-SA 4.0 <>, via Wikimedia Commons)


Black Hills Central Railroad 2-6-6-2PT Pannier Tank Mallet, July 15, 2004.

Built by The Baldwin Locomotive Works in 1928 for the Weyerhaeuser Timber Company of Vail, WA. Its next owner was The Rayonier Lumber Company where it received a tender from Rayonier No. 101 and was retired in 1968. This engine was later displayed at the Wasatch Mountain Railway in Heber City, Utah, and then sold to the Nevada State Railway Museum. The 110 was sold to The Black Hills Central Railroad in 1999, and was trucked from Nevada to South Dakota on four semi-trailers. Restoration on this engine by the mechanical crew of the BHC was completed in the spring of 2001. It is the only 2-6-6-2T Mallet in service in the world. (Duncharris' father, CC BY-SA 3.0 <>, via Wikimedia Commons)



United States

This wheel configuration existed on both the Norfolk and Western Railway 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 Summit and Tennessee Pass), and later added the two N&W locomotives to "beef up helper service" once again. All were retired between 1947 and 1952.

Chesapeake and Ohio 1309 is now operating on Western Maryland Scenic Railroad after a restoration completed in December 2020, replacing its companion, 734, which is undergoing evaluation for a possible return to service. It operated on its first excursion in December 2021.


AT&SF locomotive 3322, with ball-joint type flexible boiler, 1912.

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


Bellows type flexible joint on AT&SF locomotive 1159. (See page for author, Public domain, via Wikimedia Commons)


Equivalent classifications
UIC class: (1C)C1, (1'C)C1'
French class: 130+031
Turkish class: 34+34
Swiss class: 3/4+3/4
Russian class: 1-3-0+0-3-1
First known tender engine version
First use: 1910-1911
Country: South Africa
Locomotive: SAR Class MD
Railway: Central South African Railways
Designer: American Locomotive Company
Builder: American Locomotive Company


WMSR 1309 arrives at Helmstetter's Curve in LaVale, MD. (Ynot3700, CC BY-SA 4.0 <>, via Wikimedia Commons)

Postcard photo of Great Northern Railway's No. 1909 "Big Mallet" and No. 1 "William Crooks" on display at the Alaska-Yukon Pacific Exposition at Seattle in 1909. (Great Northern Railway, Public domain, via Wikimedia Commons)