Other companies followed the lead in 1905: the North Eastern and LBSCR using a compressed-air method of control and the Midland, using a cable-and-pulley mechanism. The Great Central deployed the trains in 1906, using cable controls similar to that of the Midland. By the 1920s most companies had them and they remained in use until replaced by diesel multiple units (DMUs) in the 1950s. In 1967, the Southern Region, already familiar with operating electric multiple units, applied the technique to its services from London Waterloo to Bournemouth, which were operated by electro-diesel locomotives. In the early 1970s, the Scottish Region used a system with a Class 27 locomotive at each end of a rake of coaches that had been retrofitted with the necessary 'Blue Star' multiple working cables to control the remote unit; but some problems of delay in actuation were experienced. They were replaced in 1979 by a system in which a Driving Brake Standard Open (DBSO), converted from a Mark 2, could control the Class 47/7 locomotive via computerised time-division multiplex (TDM) signalling through the train lighting circuits. This had the added benefit that intermediate carriages needed no special equipment, and was found more satisfactory. Such trains became widely used on the intensive passenger service between Edinburgh Waverley and Glasgow Queen Street. When the push–pull sets were replaced by multiple units, the DBSOs were transferred to the Liverpool Street to Norwich service, where they were modified to work with Class 86 electric locomotives. The original system of using the Blue Star multiple working was later revived after privatisation as a way of allowing locomotive-hauled stock to replace multiple units on certain routes, thus increasing capacity without the complications of having to run around or drag a dead locomotive at the rear. It was used by First North Western and Wessex Trains with Class 31s, and by Abellio Greater Anglia, Arriva Trains Northern, Northern Rail and Northern with Class 37s all with Mark 2 carriages. The same system was also adopted by Network Rail for its track observation trains, although on many trains one locomotive has recently been replaced by a DBSO modified to work with Blue Star. In 1988, 52 Mark 3 Driving Van Trailers were built by British Rail Engineering Limited to allow it to replace life expired electric locomotives on the West Coast Main Line. These operated with Mark 2 and Mark 3 sets. As part of the electrification of the East Coast Main Line, 31 Mark 4 Driving Van Trailers were built in by Metro-Cammell to operate with Mark 4s as part InterCity 225 sets.