|Number built:||1, 403 (192 7 and 8 car sets)|
|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  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 . The S Stock entered service on the Metropolitan from 2010, the District, Circle and Hammersmith & City from 2013 . 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|
 Paul Moss, London Underground (Haynes, 2014) p. 174
 Piers Connor, The London Underground Electric Train (Crowood Press, 2015) p. 175
 Ben Muldoon, London Underground Rolling Stock Guide (Ian Allan, 2014) p. 21
 "D Stock bows out", Modern Railways (April 2017) p. 14