In September 2014, South West Trains announced plans to procure a total of 30 five-car trains as a means of expanding the fleet used to operate services out of London Waterloo. As a result of significant infrastructure improvements to allow the operation of ten-car trains across large parts of the SWT network, the operator procured additional rolling stock to allow for this. SWT's fleet includes other Desiro units built by Siemens. The Class 707 was the second product purchased for use on the British network from the Desiro City range, following the purchase of the Class 700 for Thameslink. All are leased from Angel Trains. Construction of the first vehicles began in June 2015, with the first completed in March 2016. The first two Class 707 units were completed as dual-voltage units with pantographs for operation on catenary. This was a temporary arrangement for testing purposes at Siemens' Wildenrath facility from May 2016. The rest of the fleet is being delivered with just 750 V DC shoegear for use on third rail electrified lines, but all will have the ability to be modified for dual-voltage use if required in future. The first reached England on 9 December 2016. Entry into service was originally planned for July 2017, with all 30 planned to be delivered by the end of 2017. However, the first units entered service on 17 August, just 3 days before the South Western franchise was taken over by South Western Railway on 20 August 2017. Due to lower leasing costs now available, these trains will be replaced by Class 701 Aventras from December 2020. They will then be cascaded to Southeastern.
Operation
The Class 707 is intended primarily for services between London Waterloo and Windsor & Eton Riverside and London Waterloo and Weybridge via Hounslow, allowing the Class 458 units used on those services to be cascaded back to operations to Reading, which will then allow the Class 450 units to move elsewhere on the SWR network. The intention is to run these services as ten-car trains with pairs of Class 707s. However they also run on lines through to Kingston, Wimbledon, Epsom, Guildford and Woking. The Class 707 units are based at the Wimbledon Traincare depot.
Future
In April 2020, it was announced that Southeastern, as part of a new Direct Award Contract, had signed a deal to lease these units. They will be the last of the current South Western Railway suburban units to come off lease, following the '458s’ and then the ‘455s’ and ‘456s’. This is different to the original plan of letting the 707s off lease first. When announcing this contract, the Department for Transport promised there would be ‘space for thousands of extra passengers during the morning and evening peak times’.
