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First known tank engine version
First known tank engine version
First use	1916
Country	Germany
Locomotive	Saxon Class XV HTV
Railway	Royal Saxon State Railways
Designer	Heinrich Lindner
Builder	Sächsische Maschinenfabrik

Equivalent classifications
Equivalent classifications
UIC class	(C)C
French class	030+030
Turkish class	33+33
Swiss class	3/3+3/3
Russian class	0-3-0+0-3-0

0-6-6-0
	Baltimore and Ohio’s Old Maude of 1904, the first 0-6-6-0 Mallet in the United States
UIC class
Equivalent classifications
UIC class	(C)C
French class	030+030
Turkish class	33+33
Swiss class	3/3+3/3
Russian class	0-3-0+0-3-0
First use
First known tank engine version
First use	1916
Country	Germany
Locomotive	Saxon Class XV HTV
Railway	Royal Saxon State Railways
Designer	Heinrich Lindner
Builder	Sächsische Maschinenfabrik
First use
First known tender engine version
First use	1904
Country	United States of America
Locomotive	Class O Old Maude
Railway	Baltimore and Ohio Railroad

Under the Whyte notation for the classification of steam locomotives, a 0-6-6-0 wheel arrangement 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 wheels without any leading or trailing wheels. The wheel arrangement was mostly used to describe Mallet locomotive types and in some occasions, Double Fairlie locomotives.

A similar wheel arrangement exists for Double Fairlie, Meyer, Kitson-Meyer and Garratt locomotives, but on these types it is referred to as 0-6-0+0-6-0 since both engine units are pivoting.^[5]^[6]^[7]

Overview

The 0-6-6-0 wheel arrangement was used mostly on Mallet locomotives, on which the engine units were mounted either in tandem or facing each other. Double Fairlies with the 0-6-0+0-6-0 arrangement were sometimes referred to as 0-6-6-0 despite both engine units pivoting.

Usage

Canada

The only compound Mallets to operate in Canada were the R1 class 0-6-6-0 Vaughan design locomotives, with the cylinder ends of the engine units facing each other. The class was owned by the Canadian Pacific Railway 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 2-10-0 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, 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 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 on each side, each with a high-pressure cylinder for the rear and a low-pressure cylinder for the front drive.^[8]^[9]

Philippines

There were at least two examples of the type in the Philippines. One is Pampanga Sugar Mill No. 8 built by Baldwin Locomotive Works in 1917. Originally built for the Murmansk–Arkhangelsk Railway, it was not delivered due to the Russian Revolution. It has been working for the company by 1959 though its status after that remains unknown, likely scrapped.^[10]

No. 7 *Siete* located at the plaza of Sagay

The other is Insular Lumber Company No. 7 Siete. Another Baldwin locomotive built in 1925. It remains the sole articulated locomotive to be preserved in the country as well as the largest to be preserved, now located in the plaza of Sagay, Negros Occidental.^[11]

United States

The first Mallet locomotive in North America was built in the United States and was of this type, the Baltimore and Ohio Railroad Class O no. 2400. Nicknamed Old Maude after a cartoon mule, it had a 71,500 pounds-force (318 kilonewtons) tractive effort and was a great success despite a top speed of only 21 miles per hour (34 kilometres per hour).

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

The Kansas City Southern Railway 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 short tons (236 long tons; 239 t). They were all converted to 0-6-6-0 locomotives for heavy switching.

References

^ Sagle, Laurence W. (1964). B&O Power: Steam, Diesel and Electric Power of the Baltimore and Ohio Railroad, 1829-1964. Alvin F. Staufer. p. 168. ISBN 0-944513-06-9.
^ Bruce, Alfred W. (1952). The Steam Locomotive in America. New York: Crown (Bonanza Books). p. 314.
^ Sagle (1964). B&O Power... p. 168.
^ Bruce (1952). The Steam Locomotive in America. p. 314.
^ 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.
^ Holland, D.F. (1971). Steam Locomotives of the South African Railways. Vol. 1: 1859–1910 (1st ed.). Newton Abbott, England: David & Charles. pp. 25–27. ISBN 978-0-7153-5382-0.
^ Dulez, Jean A. (2012). Railways of Southern Africa 150 Years (Commemorating One Hundred and Fifty Years of Railways on the Sub-Continent – Complete Motive Power Classifications and Famous Trains – 1860–2011) (1st ed.). Garden View, Johannesburg, South Africa: Vidrail Productions. p. 21. ISBN 9 780620 512282.
^ Näbrich, Fritz; Meyer, Günter; Preuß, Reiner (1984). Lokomotiv-Archiv Sachsen 1 (in German). Berlin: transpress VEB Verlag für Verkehrswesen.
^ Weisbrod, Manfred; Müller, Hans; Petznick, Wolfgang (1994). Deutsches Lok-Archiv: Dampflokomotiven 3 (Baureihen 61 - 98) (in German). Berlin: transpress. ISBN 3-344-70841-4.
^ Small, Charles (1971). Rails to the setting sun. Tokyo, Japan: Kigei Publishing.
^ Llanso, Steve. "Insular Lumber Company Articulated Locomotives in [the] Philippines".