class-205-thumper

The BR Class 205 'Thumper' was a family of three-car diesel-electric multiple unit sets built by British Railways Eastleigh Works between 1957 and 1962 for the Southern Region's non-electrified rural routes in Hampshire, Sussex, and Kent — the lines that ran through the South Downs, the Weald, and the Hampshire countryside that the SR's third-rail electrification had not reached. The Thumper nickname derived from the distinctive thump of the English Electric 4SRKT diesel engines under the floor, an instantly recognisable sound that identified these units to anyone who had travelled on them.

The Class 205 used diesel-electric transmission rather than the mechanical transmission of the contemporary first-generation DMU classes — diesel engines powering generators that supplied traction motors on the wheels — which gave it the smoother, more controllable acceleration of electric traction and made it better suited to the Southern Region's tradition of electric multiple unit operation. The Class 205 could be and frequently was operated in conjunction with electric multiple units on services that included both electrified and non-electrified sections, the diesel-electric unit working through the non-wired sections while the electric units provided the power on the wired sections.

The Class 205 gave long and reliable service on Southern Region rural routes, surviving until the late 1980s and early 1990s when replacement by Class 159 and Class 171 units displaced them. Three examples are preserved: 205025, 205028, and 205205.