The British Rail Class 450 third rail DC EMU (or 4Des) began service during 2003. They are a part of the Siemens "Desiro" modular train family and are more popularly known as the 'Blue Desiro'. In standing with requirements of all new rolling stock for the South East region, provision has been made for future conversion to 25 kV AC overhead supply or dual voltage, although at present no trains have been fitted with a pantograph. Used for outer suburban services, the Class 450 is fitted with Standard and First accommodation. The unit has a maximum speed of .