The Southern Railway ( SR ) gave the designations 4Cor , 4Res , 4Buf and 4Gri to the different types of electric multiple unit built to work the route between London Waterloo and Portsmouth Harbour . The Southern Railway ( SR ) gave the designations 4-COR , 4-RES , 4-BUF and 4-GRI to the different types of electric multiple unit built to work the route between London Waterloo and Portsmouth Harbour .