During November 2014, Vivarail purchased 150 driving motor cars and 300 carriages of London Underground D78 Stock, which has been replaced by S Stock before the end of their lifespan, so that the subsurface lines (Circle, District, Hammersmith & City and Metropolitan) could have a common rolling stock fleet compatible with a new ATO system.
The stated purpose of the D-train is to ameliorate a perceived shortage of affordable, modern rolling stock on Britain's regional rail routes, resulting from the slow pace of electrification.
In the conversion programme, the company re-uses the aluminium bodyshells, traction motors and bogies from the D78 units, and fits them out with new diesel engines and interiors.

Two prototype units are being operated by Vivarail, designated as 230001 and 230002.
The diesel-electric multiple unit (DEMU) 230001 is a three-car unit; each of these is outfitted with passenger fitting and fixtures, including seats, tables, a single toilet, onboard Wi-Fi, and electrical charging points.
230001 retains the original Brush DC traction motors, however future units will make use of TSA AC motors.

Unit 230002, which was completed during 2018, is a Battery electric multiple unit, designed for operating on partially electrified routes.
It features four 106 kWh battery rafts, which provide for an operational range of 40 miles (64 km), requiring an eight-minute charge after each journey.
The battery-powered train can be charged through an automatic charging point.
Alternative means of charging the two-car vehicle include the use of a static battery bank to provide an electric supply of either 11 kV or 33 kV. Reportedly, the train requires a minimum of 750 V to operate.

The first D78 units were delivered to Vivarail on 19 January 2015; conversion of a single car prototype to facilitate testing and marketing activities commenced shortly thereafter.
By summer 2016, this prototype have been completed and was running live tests upon Vivarail's own 2.5-mile (4.0 km) test track.
During November 2016, main line testing of the units began, the prototype unit being based at the Tyseley Locomotive Works while it was operating to and from Leamington Spa railway station.
In December 2016 one of the units caught fire during testing, leading to the postponement of further trials.
During March 2017, it was announced that testing of the battery-powered demonstrator had commenced at the Quinton Rail Technology Centre.
In February 2018, Vivarail announced that its first two-car battery unit was approaching completion and was projected to run on the main line network during that summer.

The first unit entered service with West Midlands Railway on 23 April 2019.
almost exactly two years after the last D78 Stock ran on the London Underground on 21 April 2017.
During November 2014, Vivarail purchased 150 driving motor cars and 300 carriages of London Underground D78 Stock, which has been replaced by S Stock before the end of their lifespan, so that the subsurface lines (Circle, District, Hammersmith & City and Metropolitan) could have a common rolling stock fleet compatible with a new ATO system. The stated purpose of the D-train is to ameliorate a perceived shortage of affordable, modern rolling stock on Britain's regional rail routes, resulting from the slow pace of electrification. In the conversion programme, the company re-uses the aluminium bodyshells, traction motors and bogies from the D78 units, and fits them out with new diesel engines and interiors.
Two prototype units are being operated by Vivarail, designated as 230001 and 230002. The diesel-electric multiple unit (DEMU) 230001 is a three-car unit; each of these is outfitted with passenger fitting and fixtures, including seats, tables, a single toilet, onboard Wi-Fi, and electrical charging points. 230001 retains the original Brush DC traction motors, however future units will make use of TSA AC motors.
Unit 230002, which was completed during 2018, is a Battery electric multiple unit, designed for operating on partially electrified routes. It features four 106 kWh battery rafts, which provide for an operational range of 40 miles (64 km), requiring an eight-minute charge after each journey. The battery-powered train can be charged through an automatic charging point. Alternative means of charging the two-car vehicle include the use of a static battery bank to provide an electric supply of either 11 kV or 33 kV. Reportedly, the train requires a minimum of 750 V to operate.
The first D78 units were delivered to Vivarail on 19 January 2015; conversion of a single car prototype to facilitate testing and marketing activities commenced shortly thereafter. By summer 2016, this prototype have been completed and was running live tests upon Vivarail's own 2.5-mile (4.0 km) test track. During November 2016, main line testing of the units began, the prototype unit being based at the Tyseley Locomotive Works while it was operating to and from Leamington Spa railway station. In December 2016 one of the units caught fire during testing, leading to the postponement of further trials. During March 2017, it was announced that testing of the battery-powered demonstrator had commenced at the Quinton Rail Technology Centre. In February 2018, Vivarail announced that its first two-car battery unit was approaching completion and was projected to run on the main line network during that summer.
The first unit entered service with West Midlands Railway on 23 April 2019. almost exactly two years after the last D78 Stock ran on the London Underground on 21 April 2017.
British Rail Class 230