These units were wooden-bodied and were based on the prototype A Stock.
The trailers had wooden underframes as well as wooden bodywork. This proved to be insufficiently robust, resulting in their premature withdrawal. The B Stock motor cars (with steel underframes) were therefore modified as trailers in the early 1920s, the electrical equipment being used for new G Stock motor cars.
As originally built, the B Stock cars had air-operated sliding doors. This proved to be unreliable and was quickly modified to a hand-operated system, with balancing weights. The hand-operated doors could be opened by passengers whilst a train was in motion. This potentially dangerous system remained in use on some District line trains until the late 1950s. The remaining B Stock cars were later reclassified as H Stock. Following their withdrawal (by the mid-1940s) all other remaining District line trains with hand-operated doors were designated as H Stock.
The final cars were withdrawn by the 1940s. Afterwards, at least three cars were transferred into departmental service, being used as a weed killing train. No vehicles have survived into preservation.
References
Hardy, Brian (2002). underground Train File - Surface Stock 1933 - 1959. Capital Transport. ISBN1-85414-247-X.