London Transport operated locomotive hauled rolling stock on the Metropolitan line until the early 1960s. These carriages were inherited from the Metropolitan Railway in 1933. The majority were of the Metropolitan Railway's "Dreadnought" type, a design dating from the early years of the 20th century. The carriages had round topped doors, to reduce the risk of damage in the event of a door being accidentally opened in the tunnels. Some of the carriages were later converted to electric multiple unit operation, becoming T Stock.