While most regional divisions of the British Railways procured diesel-mechanic multiple units from 1957, the Southern Region built diesel-electric multiple units. The English Electric 4SRKT with turbocharger and 600 hp was used as the engine. The nickname “Thumper” came about because of the exhaust sound of the big four-cylinder. Two- and three-car units had a total of one engine and six-car units had two engines. For faster passenger exchange, some cars had doors in each compartment. The 201 to 204 and 206 classes were retired between the late 1980s and early 1990s and the 205 and 207 classes remained in service until 2004.