The 750V dc four-car trains were built in 1982-85 and refurbished in 2004-08. The fleet is currently undergoing C6 overhauls, which include modifications to comply with the European TSI for Persons with Reduced Mobility (PRM TSI).

As the class 455s are considered to have a long service life, Porterbrook and South West Trains have agreed to completely replace the DC traction systems in a project which is said to offer a lower-cost alternative to procuring new trains.

The switch to AC traction equipment and solid state inverters is expected to generate energy savings of more than 20% and will increase the maintenance interval from 16,000km to around 24,000km, freeing up capacity at Wimbledon depot to accommodate expansion of the South West Trains fleet.

The first sets will be completed in late 2014 and the entire fleet will be equipped with IGBT traction by February 2016. Porterbrook says that only two trains will be out of service for conversion at any one time, and installation will take only six days to complete when the programme is up to speed.