The British Rail Class 205 (3H) diesel-electric multiple units were built by BR at Eastleigh from 1957 to 1962, and in service for 47 years from BR Southern Region to Connex South Central and finally to the Southern franchise.

The Southern Region class 201 to 207 DEMUs are nicknamed 'Thumpers' owing to the noise they made while in motion.

They were built for services in Hampshire on the non-electrified routes between Portsmouth Harbour, Salisbury and Andover and between Alton, Winchester and Southampton Terminus.

[5] Power car (one per set) Number 1129 was experimentally fitted with a Dorman 12QTCW V-12 diesel engine of 725 shp (541 kW) The first examples of the class entered service in September 1957 after a month of testing.

The new services proved so popular that the class was temporarily taken off the route to Alton and Andover to provide extra capacity on the other lines prior to the fitting of a third carriage to the first 18 units.

[5] The delivery of the second batch of four units saw the class introduced to the Marshlink Line between Ashford and Hastings.

In 1973 some services from Portsmouth to Bristol Temple Meads and Weston-super-Mare were converted to Class 205 operation.

[5] Soon after introduction, an orange "V" shape was painted on the motor-coach in order to provide an early visual indication to station staff that there was no brake van at the other end of the unit.

With the introduction of yellow warning panels the orange V was replaced by an inverted black triangle; this being extended at this time to all Southern Region two- and three-car multiple units.

The privatisation of British Rail in 1995/6 saw the surviving Class 205s, most of which now carried Network SouthEast livery, pass to the new Connex South Central franchise.