South London commuter rail services, operated by the London, Brighton and South Coast Railway, were electrified from 1908 using overhead AC power. The implementation was carried out with 6,700 volts by the German AEG. As vehicles for these routes, three-car multiple units were ordered from the Metropolitan Carriage & Wagon Co. Ltd., now known as Metro-Cammell. Because of the competition from the new tram lines, only eight trains were ordered. Each initially consisted of two third-class railcars and a first-class intermediate car. All axles of the power cars were powered by an 115 hp motor.

Later, the trailers were removed and used in locomotive-hauled trains. At the same time, 14 mixed-class driving trailers were manufactured, each coupled to one of the power cars. The two additional power cars were provided as a reserve because they required more maintenance than the driving trailers. From 1928 the routes in south London were operated on 660 volts direct current from a conductor rail, similar to the current system. The Southern Railway, which had operated these routes since 1923, converted the vehicles for the DC system. These units, known as 2SL, each consisted of two former power cars, but only one bogie of one of the vehicles was powered. They were in use until 1954.