LB&SCR J1 class

A tank locomotive or tank engine is a steam locomotive which carries its water in one or more on-board water tanks, instead of a more traditional tender. Most tank engines also have bunkers (or fuel tanks) to hold fuel; in a tender-tank locomotive a tender holds some or all of the fuel, and may hold some water also.

There are several different types of tank locomotive, distinguished by the position and style of the water tanks and fuel bunkers. The most common type has tanks mounted either side of the boiler. This type originated about 1840 and quickly became popular for industrial tasks, and later for shunting and shorter-distance main line duties.

Tank locomotives have advantages and disadvantages compared to traditional locomotives that required a separate tender to carry needed water and fuel.



Drawing of the Novelty showing the large well tank between the wheels and below the frame

The first tank locomotive was the Novelty that ran at the Rainhill Trials in 1829.[1] It was an example of a well tank. However, the more common form of side tank date from the 1840s; one of the first of these was supplied by George England and Co. of New Cross to the contractors building the Seaford branch line for the London Brighton and South Coast Railway in 1848.[2] In spite of the early belief that such locomotives were inherently unsafe,[3] the idea quickly caught on, particularly for industrial use and five manufacturers exhibited designs at The Great Exhibition in 1851. These were E. B. Wilson and Company, William Fairbairn & Sons, George England, Kitson Thompson and Hewitson and William Bridges Adams.[4] By the mid-1850s tank locomotives were to be found performing a variety of main line and industrial roles, particularly those involving shorter journeys or frequent changes in direction.

Types of tank locomotive

There are a number of types of tank locomotive, based on the location and style of the water tanks. These include the side tank, the saddle tank, the pannier tank, the well tank and others.

Side tank

Side tanks are cuboid-shaped tanks which are situated on both sides of the boiler, extending all or part of the boiler's length.[5] The tank sides extend down to the running platform, if such is present, for at least part of their length.[6] This was a common configuration in the UK.

The length of side tanks was often limited in order to give access to the valve gear (inside motion). Tanks that ran the full length of the boiler provided greater water capacity and, in this case, cut-outs in the rectangular tank gave access to the valve gear. Longer side tanks were sometimes tapered downwards at the front to improve forward visibility. Side tanks almost all stopped at, or before, the end of the boiler barrel, with the smokebox protruding ahead. A few designs did reach to the front of the smokebox and these were termed 'flatirons'.[citation needed]

Saddle tank

The water tank sits on top of the boiler like a saddle sits atop a horse.[5] Usually, the tank is curved in cross-section, although in some cases there were straight sides surmounted by a curve (like an inverted 'U'), or even an ogee shape (a concave arc flowing into a convex arc).[7] Walter Nielson patented the saddle tank arrangement in 1849.[8]

Saddle tanks were a popular arrangement especially for smaller locomotives in industrial use. It gave a greater water supply, but limited the size of the boiler and restricted access to it for cleaning. Furthermore, the locomotive has a higher centre of gravity and hence must operate at lower speeds. The driver's vision may also be restricted, again restricting the safe speed.

The squared-off shape of the Belpaire firebox does not fit easily beneath a saddle tank, and so most saddle tanks retained the older round-topped boiler instead. A few American locomotives used saddle tanks that only covered the boiler barrel, forward of the firebox.

Water in the tank is slightly pre-heated by the boiler, which reduces the loss of pressure found when cold feedwater is injected into the boiler. However, if the water becomes too hot, injectors lose efficiency and can fail. For this reason, the tanks often stopped short of the hotter and uninsulated smokebox.

Media related to Saddle tank locomotives at Wikimedia Commons

Pannier tank

A GWR 57xx class pannier tank locomotive

Pannier tanks are box-shaped tanks carried on the sides of the boiler, not carried on the locomotive's running plates. This leaves a space between the tanks and the running plate. Pannier tanks have a lower centre of gravity than a saddle tank, whilst still giving the same easy access to the valve gear. Pannier tanks are so-named because the tanks are in a similar position to the panniers on a pack animal.[9]

Media related to Pannier tank locomotives at Wikimedia Commons


In Britain, pannier tank locomotives were used almost exclusively by the Great Western Railway. The first Great Western pannier tanks were converted from saddle tank locomotives[10] when these were being rebuilt in the early 1900s with the Belpaire firebox. There were difficulties in accommodating the flat top of the latter within an encircling saddle tank which cut down capacity and increased the tendency to overheat the water in the tank.[11] Pannier tank locomotives are often seen as an icon of the GWR.[citation needed]


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In Belgium, pannier tanks were in use at least since 1866, once again in conjunction with Belpaire firebox. Locomotives were built for the Belgian State and for la Société Générale d'Exploitatation (SGE), a private company grouping smaller secondary lines.[12]

United States

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In Logging railroads in the Western USA used 2-6-6-2 Saddle tanks or Pannier tanks for heavy timber trains.

Well tank

In this design, used in earlier and smaller locomotives, the water is stored in a 'well' on the underside of the locomotive, generally between the locomotive's frames. This arrangement was patented by S.D. Davison in 1852.[13] This does not restrict access to the boiler, but space is limited there, and the design is therefore not suitable for locomotives that need a good usable range before refilling. The arrangement does, however, have the advantage of creating a low centre of gravity, creating greater stability on poorly laid or narrow gauge tracks. The first tank locomotive, Novelty, was a well tank.

Media related to Well tank locomotives at Wikimedia Commons

Rear tank (or back tank)

A Finnish Steam Locomotive Class F1 rear tank locomotive

In this design, the tank is placed behind the cab, usually over a supporting bogie.[14] This removes the weight of the water from the driving wheels, giving the locomotive a constant tractive weight. The disadvantage is a reduction in water carrying capacity. A rear tank is an essential component of the American Forney type of locomotive, which is a 4-4-0 American-type with wheels reversed.

Wing tank

Wing tank locomotive Dougal on the Welshpool and Llanfair Light Railway

"Wing tank" redirects here. Not to be confused with Winged tank. For the auxiliary fuel tank of an aircraft, see Drop tank.

This section needs expansion. You can help by adding to it. (April 2020)

Wing tanks are side tanks that run the length of the smokebox, instead of the full length of the boiler.[15] In the early 19th century the term "wing tank" was sometimes used as a synonym for side tank.[16]

Wing tanks were mainly used on narrow gauge industrial locomotives that could be frequently re-filled with water and where side or saddle tanks would restrict access to valve gear. The Kerry Tramway's locomotive Excelsior has been described, by various sources, as both a wing tank and an inverted saddle tank.[17]

Inverted saddle tank

Joan on the Golden Valley Light Railway showing the inverted saddle tank around the smokebox

The inverted saddle tank was a variation of the Wing Tank where the two tanks were joined underneath the smokebox and supported it.[18] This rare design was used for the same reasons as the wing tank but provided slightly greater water capacity. The Brill Tramway locomotive Wotton is believed[by whom?] to have had an inverted saddle tank. The inverted saddle tank was a speciality of W.G.Bagnall.[19]


Ffestiniog Railway tender-tank locomotive Welsh Pony

A tank locomotive may also haul a tender behind it.[20] This was the common arrangement on the largest locomotives, as well as on narrow gauge railways where the small size of the locomotive restricts the space available for fuel and water. These combined both fuel and water in a proportion (where coal was used) of 1 pound of coal for every 6 pounds of water.[citation needed].

Where a tender was used with a narrow-gauge locomotive it usually carried only fuel, with water carried in the locomotive's tanks. The tender offered greater fuel capacity than a bunker on the locomotive and often the water capacity could be increased by converting redundant bunker space into a water tank.


The LSWR 415 class combined side tanks and a well tank

Large side tank engines might also have an additional rear tank (under the coal bunker), or a well tank (between the frames).[21] This may have been to increase the water capacity, to equalise the weight distribution, or else improve the stability by lowering the centre of gravity.[22]

Locomotive classification and wheel arrangement

Because tank locomotives are capable of running equally fast in both directions (see below) they usually have symmetrical wheel arrangements to ensure the same ride and stability characteristics regardless of the direction travelled, producing arrangements with only driving wheels (e.g. 0-4-0T and 0-6-0T) or equal numbers of leading and trailing wheels (e.g. 2-4-2T and 4-6-4T).[23] However other requirements, such as the need to support a large bunker, would require a non-symmetrical layout such as 2-6-4T.

Whyte classification

Main article: Whyte notation § Suffixes

In the Whyte notation for classification of locomotives (primarily by wheel arrangement), various suffixes are used to denote tank locomotives:[24]

Suffix Meaning Example
T Side tank locomotive 0-6-0T
RT Rear tank locomotive 0-4-4RT
ST Saddle tank locomotive 0-6-0ST
WT Well tank locomotive 0-6-0WT
PT Pannier tank locomotive 0-6-0PT
CT Crane tank locomotive 0-6-0CT
IST Inverted saddle tank locomotive 0-6-0IST
T+T Tender-tank locomotive 0-4-0T+T

UIC classification

Main article: UIC notation § Structure

In the UIC notation which also classifies locomotives primarily by wheel arrangement, the suffix 't' is used to denote tank locomotives[25]

Fuel bunker

Main article: Fuel bunker

On tank locomotives which use solid fuels such as coal, a bunker is used to carry the fuel (for locomotives using liquid fuel such as oil, a Fuel tank is used). There are two main positions for bunkers on tank locomotives: to the rear of the cab (as illustrated in the left of the images below), a position typically used on locomotives with a trailing carrying axle or a trailing bogie; or on top of and to one side of the firebox, a positioning typically used in cases where the firebox overhangs the rear driving axle, as this counterbalances the overhanging weight of the firebox, stabilising the locomotive.[26]

Other types of tank locomotive

There are several other specialised types of steam locomotive which carry their own fuel but which are usually categorised for different reasons.

Garratt locomotive

South African Railways NGG16 class Garratt, preserved in Wales.

Main article: Garratt locomotive

A Garratt locomotive is articulated in three parts. The boiler is mounted on the centre frame without wheels, and two sets of driving wheels (4 cylinders total) carrying fuel bunkers and water tanks are mounted on separate frames, one on each end of the boiler.[27] Articulation is used so larger locomotives can go around curves which would otherwise restrict the size of rigid framed locomotives. One of the major advantages of the Garratt form of articulation is the maintenance of the locomotive's centre-of-gravity over or inside the track centre-line when rounding curves.[28]

Crane tank locomotive

A crane tank preserved as a static exhibit at Bressingham

Main article: Crane tank locomotive

A crane tank (CT) is a steam tank locomotive fitted with a crane for working in railway workshops or other industrial environments. The crane may be fitted at the front, centre or rear.[29]

Streamlined tank locomotive

Hungarian Railways class 242

During the 1930s there was a trend for express passenger locomotives to be streamlined by enclosed bodyshells. Express locomotives were nearly all tender locomotives, but a few fast tank engines were also streamlined, for use on high-speed, but shorter, services where turn-around time was important and the tank engine's independence from turntables was useful.[citation needed] Examples included the German Class 61[30] and the Hungarian Class 242.[31]

Contractor's locomotive

Small Bagnall contractor's loco, with their distinctive cylindrical firebox

The contractor's locomotive was a small tank locomotive specially adapted for use by civil engineering contractor firms engaged in the building of railways. The locomotives would be used for hauling men, equipment and building materials over temporary railway networks built at the worksite that were frequently re-laid or taken up and moved elsewhere as building work progressed. Contractor's locomotives were usually saddle or well tank types (see above) but required several adaptations to make them suitable for their task. They were built to be as light as possible so they could run over the lightly built temporary rails and had deeply flanged wheels so they did not de-rail on the tracks which were often very uneven.[6]

At the same time, they had to be very powerful with good traction as they would often have to haul trains of wagons up very steep gradients, such as the sides of railway embankments or spoil heaps. Many were designed so that large iron ballast blocks could be fitted to the frames when extra weight and traction was required, then removed when it was not. Most had sanding gear fitted to all wheels for maximum traction. Some method of keeping mud and dust from clogging the wheels and brake shoes was also required – this either took the form of scraper bars fitted to the leading edge of the wheels or wheel washer jets supplied from the water tank. To handle long trains of loose-coupled (and often un-sprung) wagons, contractor's locomotives usually had very effective steam-powered brakes. Most lacked a full cab, often only having a front 'spectacle plate'. If a cab was provided it was usually removable along with the chimney, and sometimes the dome, so that the locomotive could be loaded onto a flatbed wagon for transport to new locations by rail whilst remaining within the loading gauge.[32]

Steam tram engines

Steam tram locomotive of Geldersche Tramwegen, Netherlands

Steam tram engines, which were built, or modified, to work on a street, or roadside, tramway were almost universally also tank engines.[33]

Tram engines had their wheels and motion enclosed to avoid accidents in traffic. They often had cow catchers to avoid road debris causing a derailment. Some tram engines were fitted with a roof and enclosed sides, giving them an appearance more like a goods wagon than a locomotive.[34]

Vertical boiler locomotives

Vertical boiler locomotive "Taffy".

Main article: Vertical boiler

Railway locomotives with vertical boilers universally were tank locomotives. They were small, cheaper-to-operate machines mostly used in industrial settings.[35]

Advantages and disadvantages

600 mm (1 ft 11+58 in) gauge tank locomotive Tx26-423 in Poznań, Poland

The benefits of tank locomotives include:

LB&SCR L class locomotives were fitted with well tanks and part of the side tanks were blanked off to improve stability

There are disadvantages:


Worldwide, tank engines varied in popularity. They were more common in areas where the length of run was short, and a quick turn around time was needed or turning facilities were not available, mostly in Europe. With their limited fuel and water capacity, they were not favoured in areas where long runs between stops were the norm.

They were very common in the United Kingdom, France, and Germany. In the United Kingdom, they were frequently used for shunting and piloting duties, suburban passenger services and local freight. The GWR was famous for its Prairie tanks (such as the "61xx" class), used for many things including very heavy trains on the Welsh valley coal mining lines that the GWR 4200 Class 2-8-0T were designed for.[40] In Germany, too, large tank locomotives were built.[41] In the United States they were used for push-pull suburban service, switching in terminals and locomotive shops, and in logging, mining and industrial service.[42]

See also


  1. ^ Kalla-Bishop, P. M.; Greggio, Luciano (1985). Steam Locomotives. Crescent Books.
  2. ^ The Industrial Locomotive Society (1967), Steam locomotives in industry, Newton Abbot: David and Charles, pp. 9–10
  3. ^ "Calamitous fire", Daily News, no. 1975, London, September 20, 1852
  4. ^ "The Great Exhibition", The Morning Chronicle, no. 26429, London, August 29, 1851
  5. ^ a b Joseph Gregory Horner (1892). Lockwood's Dictionary of Terms Used in the Practice of Mechanical Engineering. Crosby, Lockwood and Son. p. 413.
  6. ^ a b Locomotive Cyclopedia of American Practice. Simmons-Boardman Publishing Corporation. 1922. p. 86.
  7. ^ Gordon Edgar (15 October 2019). Industrial Locomotives & Railways of Scotland. Amberley Publishing. p. 220. ISBN 978-1-4456-4943-6.
  8. ^ George Augustus Nokes (1899). The Evolution of the Steam Locomotive (1803 to 1898). Railway Publishing Company. p. 11.
  9. ^ Robin Jones (31 January 2014). Great Western Railway Pannier Tanks. Crowood. ISBN 978-1-84797-654-3.
  10. ^ "Pannier tanks". Archived from the original on 2016-05-14.
  11. ^ Holcroft, H: An outline of Great Western locomotive practice 1837–1947 Locomotive Publishing Company, London, U.K. (1957), p. 42
  12. ^ Dambly, Phil: "Nos inoubliables 'Vapeur'. Editions LE RAIL, Brussels (1968)
  13. ^ "An old "well" tank locomotive". Locomotive, Railway Carriage and Wagon Review. Locomotive Publishing Company. 1908. p. 218.
  14. ^ "Tank locomotives for suburban service on American railways". Engineering News. McGraw-Hill Publishing Company. 1905. p. 168.
  15. ^ Nehemiah Hawkins (1909). Hawkins' Mechanical Dictionary: A Cyclopedia of Words, Terms, Phrases and Data Used in the Mechanic Arts, Trades and Sciences. T. Audel. p. 655.
  16. ^ Institution of Mechanical Engineers (Great Britain) (1864). Proceedings of the Institution of Mechanical Engineers. The Institution. p. 103.
  17. ^ Cozens, Lewis (1953). The Van and Kerry Railways: With the Kerry Tramway. R. Cozens.
  18. ^ Mark Smithers (31 March 2016). The Royal Arsenal Railways: The Rise and Fall of a Military Railway Network. Pen & Sword Books. p. 192. ISBN 978-1-4738-4401-8.
  19. ^ "Narrow Gauge Locomotive For the Gas Light and Coke Company". Engineering. 7 June 1895.
  20. ^ Anthony Burton; John Scott-Morgan (30 November 2015). The Light Railways of Britain and Ireland. Pen and Sword. pp. 18–19. ISBN 978-1-4738-2706-6.
  21. ^ Lowe, James W. (2014). British Steam Locomotive Builders. Pen & Sword Books Limited. ISBN 978-1-4738-2289-4.
  22. ^ "Locomotives built between 1930 and 1962". Trains. Vol. 24. Kalmbach Publishing Company. 1964. p. 35.
  23. ^ Joseph Russell Howden (1909). The Boys' Book of Locomotives. F. A. Stokes Company. pp. 177–179.
  24. ^ Industrial Locomotives: including preserved and minor railway locomotives. Vol. 17EL. Melton Mowbray: Industrial Railway Society. 2015. ISBN 978 1 901556 88 9.
  25. ^ Standard designation of axle arrangement on locomotives and multiple-unit sets. [ Obligatory ] (5 ed.). 1 January 1983. ((cite book)): |work= ignored (help)
  26. ^ Henry Greenly (1904). The Model Locomotive: Its Design and Construction; a Practical Manual on the Building and Management of Miniature Railway Engines. P. Marshall & Company. p. 35.
  27. ^ Nock, O.S (1971). Railways in the Years of Pre-Eminence 1905–19. Blandford Press. p. 127.
  28. ^ A. E. Durrant (1969). The Garratt Locomotive. David & Charles. ISBN 978-0-7153-4356-2.
  29. ^ Locomotive Magazine and Railway Carriage & Wagon Review. Locomotive Publishing Company. 1907. p. 47.
  30. ^ Gottwaldt, Alfred (2005). Die Baureihe 61 und der Henschel-Wegmann-Zug (in German). Freiburg: EK-Verlag. ISBN 978-3-88255-161-7.
  31. ^ Kubinszky, Mihály (1975). Ungarische Lokomotiven und Triebwagen (in Hungarian). Budapest: Akadémiai Kiadó. ISBN 963-05-0125-2.
  32. ^ John K. Brown (September 2001). The Baldwin Locomotive Works, 1831–1915: A Study in American Industrial Practice. JHU Press. ISBN 978-0-8018-6812-2.
  33. ^ Barcroft, Henry (1881). Steam Tramways: a Pressing Want of the Times. Hodges, Figgis.
  34. ^ Clark, Daniel Kinnear (1894). Tramways, Their Construction and Working, Embracing a Comprehensive History of the System, Accounts of the Various Modes of Traction. C. Lockwood and son.
  35. ^ Abbott, Rowland Aubrey Samuel; Lowe, James Wensley (1989). Vertical Boiler Locomotives and Railmotors Built in Great Britain. Oakwood Press. ISBN 978-0-85361-385-5.
  36. ^ Camp, Walter Mason, ed. (22 April 1905). "Meeting of Western Railway Club". The Railway and Engineering Review. XLV (16). Railway Review, Incorporated: 283.
  37. ^ Western Railway Club (1904). Official Proceedings. Western Railway Club. p. 2.
  38. ^ "6-wheeled tank locomotive, D.W. & W. Ry". Locomotive, Railway Carriage and Wagon Review. Locomotive Publishing Company. 13 June 1903. pp. 404–406.
  39. ^ Bradley, D.L. (1974). Locomotives of the London Brighton and South Coast Railway: Part 3. Railway Correspondence and Travel Society.
  40. ^ "The 4200 class GWR Tank locomotives". The Great Western Archive.
  41. ^ De Cet, Mirco; Kent, Alan (2006). The Complete Encyclopedia of Locomotives. Rebo International B.V. pp. 74–78. ISBN 978-90-366-1505-1.
  42. ^ John H. White (1 January 1979). A History of the American Locomotive: Its Development, 1830–1880. Courier Corporation. pp. 233–235. ISBN 978-0-486-23818-0.