The class 769 trains have been converted from class 319 EMUs to operate on 25kV ac overhead and 750V dc third rail electrification as well as diesel traction. In addition, the Flex trains have been fitted with Wi-Fi, power sockets at each seat, air cooling, larger luggage racks, and new seat covers.

The trains will be introduced on the Reading - Redhill - Gatwick Airport route, which is only partly electrified, next year, followed by the Twyford - Henley and Maidenhead - Bourne End branch lines and between Reading and Basingstoke.

As the trains enter service, GWR will transfer its Turbo DMUs to the Bristol area.