London Underground S7/S8 Stock

The S Stock fleet is a standard fleet of trains for London Underground's sub-surface lines, the order for over 1, 400 cars is probably the biggest single order for rolling stock for a British railway [1]. The S Stock has replaced A Stock on the Metropolitan Line, C Stock on the Circle and Hammersmith & City Lines and finally D Stock on the District Line in early 2017.

Number built: 1, 403 (192 7 and 8 car sets)
Built: 2009-17
Builder: Bombardier Derby
Engine: Bombardier MITRAC traction system (750v DC fourth rail)
Formation: (S7) Driving Motor (DM)+Non Driving Motor (NDM)

There are two variants, the S7 which is a 7-car unit for the Circle, District and Hammersmith & City Lines and the 8-car S8 for the Metropolitan Line. The S8 also has some transverse seating while the S7 is all longitudinal. There are 133 S7 trains and 58 S8s. There is also a single S7+1 train which is an 8-car set but has all longitudinal seating. This will be used on the Metropolitan Line's future extension to Watford Junction. The S Stock has "walk-through" open gangways throughout the train to ease passenger movement, an insulated gate bipolar transistor (IGBT) traction system [2] and regenerative braking.

The S Stock is capable of Automatic Train Operation and this will be phased in from 2018 pending signalling upgrades starting with the Western end of the Hammersmith & City [4]. The S Stock entered service on the Metropolitan from 2010, the District, Circle and Hammersmith & City from 2013 [3]. All trains will be in service by the end of 2017.
Metropolitan S8 train at Amersham

District S7 train at Acton Town

Metropolitan S8 train at Baker Street

S Stock train at Derby, en route for some modifications at Litchurch Works

Aboard a Circle Line S Stock train

Hammersmith & City S7 train at West Ham

[1] Paul Moss, London Underground (Haynes, 2014) p. 174
[2] Piers Connor, The London Underground Electric Train (Crowood Press, 2015) p. 175
[3] Ben Muldoon, London Underground Rolling Stock Guide (Ian Allan, 2014) p. 21
[4] "D Stock bows out", Modern Railways (April 2017) p. 14