A generation of tube trains known as 'Standard stock' were built between 1923 and 1934. The traction control equipment was housed behind the driver's cab and took up a lot of room.
All Standard stock cars had air-powered doors instead of attendant-controlled gates at the ends. This greatly increased the speed passengers could board at stations. Standard stock were the principal trains on the Piccadilly and Central lines until the early 1960s.