The 900 series classes were reserved for multiple units in departmental stock, most of which were converted from old passenger units. In broad terms, classes 930-935 were allocated to Southern Region multiple units (ex-200 and 400 series), 936 & 937 to other EMUs (ex-300 and 500 series) and 960 to other DMUs (ex-100 series). In recent years, this has been less rigidly adhered to.