The London Underground Q Stock were trains used on the District line of the London Underground. First introduced in 1938, these electric multiple units were formed from cars built between 1923 and 1935 and new purpose-built cars, and fitted with electro-pneumatic brakes and guard controlled air-operated doors. Trains were made up from cars of different ages with differing appearances, the older ones with clerestory roofs and the newer ones with flared sides. Some units were withdrawn in the early 1960s, although six- and eight-car trains remained on the District line with use gradually diminishing to peak hours only, and four car units worked the East London line until 1971.