The first three trains had streamlined cabs fitted at both ends of each two-car unit. The driver's seat was placed in the centre of the semi-elliptical cab, and the armchair seat had the brake and master controller handles on either side, similar to aeroplane joysticks. Drivers did not like the arrangement, and when it was shown that the streamlining would have little effect until speeds of were reached, the fourth train, which was fitted with control equipment by Metropolitan Vickers, was built with flat ends and conventional cabs, an appearance that was carried forwards to the 1938 Stock. The two-car units were fitted with Wedglock couplers at the outer ends, which were a development of the Tomlinson coupler, and joined the units mechanically, pneumatically and electrically. One unit of the first train was fitted with air conditioning and fixed windows, but this was removed and opening windows were installed, as any failure of the system resulted in the car overheating in tunnels, causing discomfort for passengers.