London Underground D78 Stock

The D78 Stock was built in the late 1970s for the District Line of London Underground replacing CO/CP and R Stock some of which had been in service since before the Second World War. The D78 (or just D) Stock bought a number of innovations with a keen eye for interior design to make them more inviting for passengers [1]. They had much improved suspension compared to earlier designs. They also introduced the twist-grip deadman joystick replacing the older style deadman button grip [2] (the deadman is a safety device which stops the train if the driver in incapacitated). One Man Operation began on the trains in 1985.

Number built: 450 (75 6-car sets)
Built: 1978-81
Builder: Metro-Cammell
Engine: Brush LT118 traction motors (630v DC third & fourth rail)
Formation: Driving Motor (DM)+Trailer (T)+
Uncoupling Non-Driving Motor (UNDM)+UNDM+T+DM
(Some sets are DM+T+DM)

The D78 Stock cars were the longest on the Underground, which proved to be a problem on the District Line's High Street Kensington - Edgware Road branch as the D78 Stock was too long (C Stock trains were used instead)! [3] Most D78 Stock formations had 2 Driving Motors (DMs) at either end with non-driving motor cars in the middle, though some had DMs in the middle meaning they could be used as 3 car sets. They were used as such for a couple of years on the East London Line in the mid-1980s.

The D78 Stock fleet received a heavy mid-life refurbishment in the 2000s but were replaced as part of London Underground's standardisation for its Surface Stock fleet. The D78 Stock's replacement by S Stock was complete in Spring 2017, a number of years earlier than planned. Some D78 Stock will live on on the National Rail network as Class 230 DMUs (or bi-mode hybrids).
7535 at West Brompton

7094 at Earls Court

7049 at Kew Gardens

Aboard a D Stock train in its latter days

[1] Paul Moss, London Underground 1863 Onwards (Haynes, 2014) p. 132
[2] Piers Connor, The London Underground Electric Train (Crowood, 2015) p. 122
[3] Ben Muldoon, London Underground Rolling Stock Guide (Ian Allan, 2014) p. 26