With the London to Portsmouth electrification in 1937 came the delivery of new main line corridor stock, classified 4COR. These four coach sets were constructed by the SR at Eastleigh Works. The external design was a break from previous styling and incorporated a central gangway, with a train reporting number position on the opposite side to the driver's front window. The four car set formation was motor brake third open (MBTO), seating 52, trailer composite (TC), accommodating passengers in five first class and three third class compartments, third corridor (TK), with eight compartments and a coupe, and a further MBTO, toilet facilities being provided in both trailer cars. The inclusion of the corridor connections on set ends provided total freedom throughout an eight or twelve car train, when two or three sets were in multiple. It also gave passenger access to refreshment facilities, usually marshalled in the centre of a formation.
Traction equipment for the COR stock consisted of four 225hp traction motors, two mounted on the outer bogies of driving cars—these were supplied by Metropolitan Vickers Ltd. Numbers allocated to the original COR sets were 3101-3129. During 1937/8, a second identical batch of COR units entered service numbered 3130-3155 for use on the Mid-Sussex electrification scheme. Three further sets were introduced in the mid-1940s, numbered 3156-58, to replace damaged stock.
COR stock normally operated on the coastal routes, usually in pairs, with a restaurant/buffet/griddle unit between. Following the introduction of new main line stock in the mid-1960s, the COR units were displaced to other duties, including the Coastway and the Waterloo to Reading/Guildford line. Stock was finally withdrawn in September 1972. From 1964, the restaurant cars were removed from six 4RES and one 6PUL unit and, after reformation, seven 4COR(N) sets entered service numbered 3065-71 for use on the Littlehampton/Worthing routes. During late 1965, ten 6COR units were introduced, being formed of redundant PUL/PAN vehicles, and numbered 3041-50. Although classified as COR units, these sets were only fitted with gangways within sets, and did not have end corridor connections. Other reformations took place in 1965 and Nos. 3159-3168 were formed from redundant RES/PUL/PAN vehicles.
To operate with COR stock on the Waterloo to Portsmouth route, fleet of 13 buffet car sets was built at Eastleigh in 1938, and numbered 3073-3085. This batch of units was of similar design to the 4COR sets, but in place of the trailer third there was a buffet car, its internal layout consisting of a service compartment, bar with stool seats, and two toilets. The service section of the car contained all cooking facilities, and power for the buffet was provided by an underslung generator set. There were two special points of interest about these sets. When built, the refreshment car was painted in Malachite green with the remainder of the unit in Brunswick green, and the bar was concave in shape.

RES, GRI.
To provide full restaurant facilities for the Portsmouth electrification, 19 four car full restaurant sets, classified as 4RES, were introduced. Sets closely resembled the COR units which they operated alongside. The two driving motor vehicles, seating 52, were constructed by the SR at Eastleigh Works, whilst the third class trailer and the first class restaurant cars were built by the Birmingham Railway Carriage & Wagon Company Ltd, and the Metropolitan Carriage, Wagon & Finance Company respectively. The restaurant vehicle was set out in five compartments, each provided with four or six loose chairs, and a dining area with 12 additional seats. The third class trailer had a small pantry, kitchen and seating area for 36. After the RES stock entered service in 1937/8, they usually operated on their intended route, often sandwiched between two 4COR units. One of the RES sets is of special interest. On set No. 3072 the restaurant car suffered considerable fire damage in 1952, and was rebuilt as a cafeteria style buffet car, the unit being reclassified as 4BUF.
RES stock remained in service until 1962, when three sets were taker out of traffic and rebuilt as griddle units; during modification work, the restaurant cars were completely rebuilt and accommodated a buffet/ kitchen and bar sections. Units converted in this way became classified as 4GRI (four car griddle). Numbering applied to RES sets was 3054-72, while those converted to GRI stock were renumbered 3086-88.