The class 159 is very similar to the 158 but was adapted for Network South East from the build originally ordered by Regional Railways. The interior layout was changed, providing a first class area and various reliability modifications have been carried out since the units entered service. The units operate primarily from Waterloo to Salisbury, where they are all allocated for maintenance. Reliability has been consistently good since their introduction in 1992 – 1993. They are fitted with the Cummins NTA 855R engine, providing 300kW (400 hp) through a Voith transmission to a Gmeinder final drive. The bodyshell is aluminium, keeping the weight down to 38 tonnes, almost 8 tons lighter than a Turbostar. Air conditioning is provided, along with air suspension and a pa system. The units are not RVAR compliant, and cannot practically be made so as the door opening is 750mm, not 800mm which is the requirement.