LNWR Dreadnought Class

The LNWR Dreadnought Class was a series of compound 2-2-2-2 express passenger locomotives designed by Francis Webb and introduced at Crewe Works from 1884, representing Webb's second attempt at a practical compound express locomotive after the relative disappointment of the earlier Experiment Class. The Dreadnought name — suggesting impregnable power — reflected the ambition of the design, and the class was Webb's most determined effort to prove that compound expansion could revolutionise the thermal efficiency of British express locomotive practice.

Webb had become obsessed with the theoretical advantages of compounding — expanding steam through high-pressure cylinders first, then re-expanding the partially-exhausted steam through larger low-pressure cylinders to extract more work from the same amount of fuel — and the Dreadnought Class represented his attempt to translate this theory into a practical express locomotive for the West Coast Main Line. The 2-2-2-2 wheel arrangement — two leading wheels, two high-pressure driving wheels, two low-pressure driving wheels, and two trailing wheels — was unique in British practice and reflected Webb's desire to keep the compound cylinders mechanically separate: the two inside high-pressure cylinders drove the rear pair of uncoupled driving wheels while the two outside low-pressure cylinders drove the front pair, with no mechanical coupling between the two sets of driving wheels.

This uncoupled arrangement, combined with the compound expansion, created a locomotive with serious operational problems. Starting from rest required the high-pressure cylinders to build up enough steam in the low-pressure circuit before the outside cylinders contributed meaningfully, meaning that the driving wheels frequently slipped independently of each other, particularly on starting. LNWR footplate staff found the Dreadnoughts difficult to manage, and the class became notorious for its inability to start reliably on grades. Stories abounded of Dreadnoughts that could be seen slipping in opposite directions simultaneously — the front and rear driving wheels rotating independently without moving the locomotive. Despite these problems, when running well the Dreadnoughts could maintain fast schedules, but the operational unreliability made them unpopular with crews and depot staff alike.

Webb built 40 Dreadnoughts between 1884 and 1888, and his successor George Whale quickly rebuilt them as simple-expansion locomotives after taking over at Crewe in 1903, substantially improving their performance and reliability. None was preserved in original Webb compound form.