In 1956, they were borrowed from British Railways to run the North Western Railway while Sir Topham Hatt's engines visited the Mainland. Jinty ran Thomas' Branch Line while Thomas was away and also helped the latter when he crashed into some buffers.
It is possible that Percy knows them from taking trains to the end of the line and telling the other engines stories, like at the beginning of Percy Takes the Plunge.
Jinty is based on an LMS 3F 0-6-0T. Pug is based on an LMS 0F Kitson 0-4-0ST. Their names originate from their classes' nicknames "Jinty" and "Pug". A total of nine 3F 0-6-0 tank engines survive in preservation whereas all 0F Kitsons were scrapped.
Jinty and Pug are painted in BR unlined black. Jinty has the BR logo painted on his side tanks. It is possible that Pug has a BR logo on his cab, though the Water Tower obscures it.
- In the second illustration of The Fat Controller's Engines, Jinty and Pug are not illustrated with faces.