The British Rail Class 159 is a class of British diesel multiple unit passenger trains of the Sprinter family, built in 1989–1992 by British Rail Engineering Limited (BREL)'s Derby Litchurch Lane Works as Class 158. Before entering traffic, the original 22 units were modified at Rosyth Dockyard to Class 159 to operate services from London Waterloo to Salisbury and Exeter St Davids, replacing various locomotive-hauled passenger trains. The units were originally branded by Network SouthEast as South Western Turbo. History and design In the late 1980s, the locomotive-hauled stock on Network SouthEast's West of England route from London Waterloo to Salisbury, Yeovil Junction and Exeter St Davids was in urgent need of replacement. The Class 50 locomotives were not suited to the stop-start nature of the route, and frequently broke down. Because of the long sections of single track west of Salisbury following the Beeching cuts, a single breakdown could cause chaos. Various options were considered including electrification, shortened HSTs, construction of new locomotives and stock (a passenger version of the proposed Class 48), or the proposed Class 171 (which would have been part of the Networker family, an intercity version of the Class 165 – not to be confused with the later Turbostars). A study found the best options were electrification or new DMUs. With the UK economy in decline in the early 1990s, it was found that Regional Railways had over-ordered Class 158s at the same time as Network SouthEast was looking for a similar number of new diesel trains. NSE agreed to take on the surplus Class 158s. The original 22 units were built as Class 158 units, but were rebuilt by Babcock Rail in Rosyth Dockyard before entering traffic. This entailed fitting first-class accommodation and retention toilets, and various other modifications. The rebuild was required because it was not possible for Network SouthEast and the newly privatised BREL to agree terms on the variation order to NSE specification. The first unit (159004) was handed over to NSE on 6 January 1993. The units converted to Class 159 specification during construction are numbered 159001–159022, with individual vehicles numbered 52873–52894 and 57873–57894 for driving motor vehicles, and 58718–58739 for intermediate motor vehicles. The entire class is maintained at a purpose-built depot at Salisbury. In 2007, eight further Class 159 units were created through the rebuilding of surplus Class 158 units displaced from TransPennine Express. The units feature BSI