2-6-6-0

2-6-6-0

Front of locomotive at left

NGR Mallet 2-6-6-0 of 1909

Equivalent classifications UIC class 1CC 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 1906 Country New Zealand Locomotive NZR E class Pearson's Dream Railway New Zealand Railways Designer G.A. Pearson Builder NZR Petone Workshops

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

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 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 In 1917, E 66 was withdrawn from service and scrapped.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.

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.

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.