Pug (steam locomotive)

'Pug' locomotives are small steam locomotives which were produced for light shunting and industrial work, often on dockyards and factory sites, such as steelworks, collieries, etc. The Pugs are named after a common term in Scotland for a small industrial shunting locomotive – typically an 0-4-0 tank. ‘Pug’ was a dialect word meaning ‘monkey’ inferring an ugly appearance. Another suggestion is that the locomotive type is named after the small sturdy 'Pug' dog, an ancient and well known breed with a snub nose, wrinkled face, and squarish body. Many were saddle tanks, with the water tank sitting on top of the boiler like a saddle.

Whilst most commonly used for small shunting engines, on some railways the term 'Pug' was used for all tank engines. For example, the very large Glasgow and South Western Railway 540 Class 4-6-4T express passenger locomotives were known to their enginemen as the 'Big Pugs'.

Many locomotive manufacturers produced Pug type locomotives mainly for shunting work and for use on industrial sites with tight curves for which 0-6-0 locomotives were less well suited, despite their greater tractive effort capabilities. The Lancashire and Yorkshire Railway L&YR Class 21 were nicknamed 'Pugs' and the Caledonian Railway built a class of 0-4-0 Pugs. The North British Railway had a class of 38 locomotives designated NBR G Class which were commonly nicknamed 'Pugs' by staff.

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