each seating bay. To prevent passengers leaning out of the opening windows, they were partially blocked with three bars — this was for passenger safety when travelling through areas with limited clearance, in particular Hampstead Tunnel. This earned them the nickname "jail units". The stock differed from that for the Southern Region in that each vehicle was long instead of , and the vehicles within the units had screw coupling with two buffers instead of the close-coupled single buffer with chain arrangement used on the Southern multiple units. Formation The trains were made up in 3-car formations as follows: Driving motor with two saloons of 3+4 bays + 9 compartment intermediate trailer + driving trailer with two saloons of 3+4 bays. Unusually for the time, the vehicles featured screw couplings both within and between the units, in contrast to the SR units which had intermediate single buffer and chain and buckeye couplings at the unit ends. Although all other areas of the London Midland region had trains with both first and second class accommodation, the inner London area had withdrawn first class from main line trains operated entirely within the London Transport boundaries as a wartime measure in 1940. It was never reinstated, so these trains were second class only. Electrical equipment The motor coaches had two powered bogies and GEC electrical equipment. They were the first to have camshaft controllers. The train ends also followed the EPB style and incorporated a two-character alphanumerical headcode. Motors There were four 185 hp GEC traction motors giving a total of 740 hp per 3-car set. Livery Initially these trains were painted in the standard mid-green livery adopted for electric multiple unit stock at nationalisation. This was replaced by a dark brunswick green livery with wide yellow bands in the early 1960s, the same livery as had been adopted for diesel multiple unit stock. In the late 1960s this was changed to rail blue, and from 1981, units sent for general overhaul received rail blue and grey livery. Modification They were never facelifted or refurbished during their career; however, during the 1970s some trains had the intermediate trailers modified from compartment layout to open saloon. This work was carried out at Croxley Green workshops and, though quite neatly done, the overhead luggage racks which had been attached to the partitions were not replaced, leaving nowhere to put things like coats and umbrellas. Withdrawal