Stephenson Long Boiler

Stephenson's 1841 patent specified a locomotive with a much longer boiler than was conventional, mounted over a short rigid wheelbase that placed all carrying and driving wheels close together. The arrangement allowed a much larger heating surface — and therefore better steam-raising — than contemporary practice, and was widely adopted by European railways for express work in the 1840s.

British practice quickly identified the layout's defect: the long boiler overhanging the short wheelbase produced severe oscillation at speed, leading to several derailments. The 2-2-2 long-boiler express engines were rapidly withdrawn from express duty after a fatal accident at Round Oak in 1858. The 0-6-0 long-boiler goods variant, however, ran at lower speeds and proved successful — long-boiler 0-6-0s were built in considerable numbers for British railways through the 1840s and 1850s.

Long-boiler express engines were progressively withdrawn from the 1850s onwards. The 0-6-0 goods variant lasted longer; the last in British service were withdrawn in the 1890s. Several long-boiler 0-6-0s are preserved on the Continent, notably at the German railway museums.

Disproportionately long boiler relative to the short rigid wheelbase, with all wheels grouped closely together near the boiler centre. The 2-2-2 variants have a single pair of drivers between leading and trailing carrying wheels close together; the 0-6-0 variant has all six wheels closely coupled.

• Various — most British examples not preserved; some Continental examples in European railway museums