 The N15 class was intended to haul heavy expresses over the long LSWR mainlines between Waterloo, Weymouth, Exeter and Plymouth. Locomotives were changed at Salisbury before the upgrading of the South Western Mainline in 1922, when fast running through to Exeter was possible. The Southern Railway's motive power re-organisation following the Grouping of 1923 saw the class allocated to sheds across the network and used on Bournemouth to Oxford cross-country trains. Operations were expanded to more restricted Central and Eastern section mainlines in 1925, and suitably modified class members hauled commuter and heavy boat trains from London Victoria to Dover Marine and expresses to Brighton. In 1931, No. E780 Sir Persant hauled the inaugural Bournemouth Belle Pullman train from Waterloo to Bournemouth West.
