When the Southern Railway had electrified the line from London Waterloo to Portsmouth Harbour via Woking, they started to build four-car electric multiple units in their own workshops at Eastleigh and Lancing. Each unit had two 225 hp traction motors in the outermost bogies. The basic variant was called 4-COR due to the number of cars and the corridor running through the whole train, including gangway doors at the ends.

Apart from 29 4-COR units, 19 4-RES units were built which included a restaurant car. Usually, twelve-car trains were formed with a 4-RES with a 4-COR on each end. When more lines had been electrified, 26 more 4-COR and 13 4-BUF were built. The latter had a cheaper buffet instead of the restaurant. In the early sixties, three units had their restaurant car rebuilt to griddle cars, what led to the designation 4-GRI. With the TOPS classification, the remaining units became class 404. The last ones were withdrawn in 1972.