The British Rail Class 171 Turbostar is a type of diesel-hydraulic multiple unit passenger train built by Bombardier Transportation at Derby Litchurch Lane Works in England.

This provision was made to allow emergency joining with Class 377 DC third-rail electric units, which Southern runs extensively on most lines.

The units work on the southern regions of the British railway system, operating services from London Bridge to Uckfield and from Eastbourne to Ashford International, these routes being unelectrified between Hurst Green Junction and Uckfield and between Ore and Ashford International, respectively.

The fleet is fitted with coupling devices (Dellner) different from other Turbostars, and is classified as Class 171 for this reason.

[6] The first units were introduced in 2003 on the Marshlink Line from Ashford to Hastings and were extended in 2005 to Brighton, but in 2018 the service was cut back to Eastbourne due to overcrowding and a shortage of additional diesel stock.

These units were often coupled together, forming six-car, eight-car or ten-car trains following platform extensions at Uckfield line stations.