London Underground Main Line Stock

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.

These carriages were used on trains between Aylesbury and London. They were hauled by electric locomatives as far north as Rickmansworth, where a change to steam haulage was made.

Some of the carriages were later converted to electric multiple unit operation, becoming T Stock.

R Stock confusion
In 1940 London Transport briefly designated some of the former Metropolitan Railway carriages as "R Stock" as a way of identifying former coaches of Metropolitan Railway saloon stock still in use, but not on Circle Line services. However withdrawal of the former MR electric multiple units was virtually complete by this point, due to age and as a consequence the title never caught on. It was subsequently reused five years later as a title for new cars of District Line stock. This was more logical as it followed on from the last new stocks (O, P and Q38), and shared a similar resemblance.

Replacement
In the early 1960s, the Metropolitan line was electrified as far north as Amersham. The locomotive hauled carriages were replaced from 1960 by new trains of London Underground A60 Stock. British Railways took over the operation of services north of Amersham and introduced the Class 115 diesel multiple units for the line.

Sources: 'Steam to Silver', J. Graem Bruce, LT pub.; 'The R Stock Story', Piers Connor, LURS pub.