Under the

Whyte notation Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth cen ...

for the classification of

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...

s, a

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

refers to a locomotive with two engine units mounted under a rigid locomotive frame, with the front engine unit pivoting and each engine unit with six coupled

driving wheel On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons (or turbine, in the case of a steam turbine locomotive). On a conventional, non-articulated locomotive, the driving wheels are all coupled ...

s without any

leading In typography, leading ( ) is the space between adjacent lines of type; the exact definition varies. In hand typesetting, leading is the thin strips of lead (or aluminium) that were inserted between lines of type in the composing stick to incr ...

or trailing wheels. The wheel arrangement was mostly used to describe

Mallet locomotive The Mallet locomotive is a type of articulated steam railway locomotive, invented by the Swiss engineer Anatole Mallet (1837–1919). The front of the locomotive articulated on a bogie. The compound steam system fed steam at boiler pressur ...

types. A similar wheel arrangement exists for

Double Fairlie A Fairlie is a type of articulated steam locomotive that has the driving wheels on bogies. The locomotive may be double-ended (a double Fairlie) or single ended (a single Fairlie). Fairlies are most famously associated with the Ffestiniog Rai ...

, Meyer, Kitson-Meyer and

Garratt A Garratt (often referred to as a Beyer Garratt) is a type of steam locomotive invented by British engineer Herbert William Garratt that is articulated into three parts. Its boiler, firebox, and cab are mounted on a centre frame or "brid ...

articulated locomotives, but on these types it is referred to as since both engine units are pivoting.Espitalier, T.J.; Day, W.A.J. (1943). ''The Locomotive in South Africa - A Brief History of Railway Development. Chapter II - The Adoption of the 3 ft. 6 in. Gauge on the Cape Government Railways'' (Continued). South African Railways and Harbours Magazine, August 1943. pp. 592-594.

Overview

The 0-6-6-0 wheel arrangement was used mostly on

Mallet A mallet is a tool used for imparting force on another object, often made of rubber or sometimes wood, that is smaller than a maul or beetle, and usually has a relatively large head. The term is descriptive of the overall size and propor ...

locomotives, on which the engine units were mounted either in tandem or facing each other.

Usage

Canada

The only compound Mallets to operate in Canada were the R1 class Vaughan design locomotives, with the cylinder ends of the engine units facing each other. The class was owned by the

Canadian Pacific Railway The Canadian Pacific Railway (french: Chemin de fer Canadien Pacifique) , also known simply as CPR or Canadian Pacific and formerly as CP Rail (1968–1996), is a Canadian Class I railway incorporated in 1881. The railway is owned by Canad ...

and served on the Big Hill in British Columbia, which had a 4.1% grade. Five locomotives were built between 1909 and 1911. A sixth one was built, but it was a simple expansion Mallet with two sets of high-pressure cylinders. All the locomotives in this class were later converted to types and were used as shunting and transfer engines in Montreal.

Germany

The Saxon Class XV HTV was a class of goods train tank steam locomotive operated by the

Royal Saxon State Railways The Royal Saxon State Railways (german: Königlich Sächsische Staatseisenbahnen) were the state-owned railways operating in the Kingdom of Saxony from 1869 to 1918. From 1918 until their merger into the Deutsche Reichsbahn the title 'Royal' was d ...

, which had been conceived for hauling trains and acting as banking engines for routes in the Ore Mountains. The two CCh4v locomotives were built in 1916 at the Sächsischen Maschinenfabrik, formerly Hartmann. In 1925, the

Deutsche Reichsbahn The ''Deutsche Reichsbahn'', also known as the German National Railway, the German State Railway, German Reich Railway, and the German Imperial Railway, was the German national railway system created after the end of World War I from the regiona ...

grouped them into their DRG Class 79.0. The locomotive was of unusual design with two fixed six-coupled engine units with a central double

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an ...

on each side, each with a high-pressure cylinder for the rear and a low-pressure cylinder for the front drive.

United States

The first

in North America was built in the United States and was of this type, the

Baltimore and Ohio Railroad The Baltimore and Ohio Railroad was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. Merchants from Baltimore, which had benefited to some extent from the construction of ...

Class O no. 2400. Nicknamed ''Old Maude'' after a cartoon mule, it had a tractive effort and was a great success despite a top speed of only . A 0-6-6-0 Mallet of the New York Central Railroad

A 0-6-6-0 Mallet of the New York Central Railroad

The Kansas City Southern used the type as freight engines, with pilots, and had the most of them with twelve locomotives. The 0-6-6-0 wheel arrangement was also used to a limited extent on logging railroads and in mountain terminals. The Western Maryland Railway had a small fleet of 2-6-6-2 locomotives which, at one time, were the heaviest locomotives in the world, weighing 264 Tons. They were all converted to 0-6-6-0 locomotives for heavy switching.

References

{{Whyte types