London Underground S7 and S8 Stock
| Industry | Rail transport manufacturing |
|---|---|
| Headquarters | Derby , United Kingdom |
| Products | S7 Stock, S8 Stock (London Underground trains) |
London Underground S7 and S8 Stock
The London Underground S7 and S8 Stock, collectively referred to as S Stock, represents a fleet of passenger trains introduced to the subsurface lines of the London Underground starting in 2010. These trains were produced by Bombardier Transportation at the Derby Litchurch Lane facility and were designed to replace the older A60/A62, C69/C77, and D78 rolling stock that had been in service on the Circle, District, Hammersmith & City, and Metropolitan lines since the 1960s and 1970s.
This procurement, valued at £1.5 billion, included a total of 192 trains consisting of 1,403 cars split into two distinct models: the S7 Stock serving the Circle, District, and Hammersmith & City lines, and the longer S8 Stock allocated to the Metropolitan line. The two variants differ primarily in train length and seating arrangements. Both types are equipped with air-conditioning systems, feature low-floor designs to enhance accessibility, and incorporate open gangways that allow passengers to move freely between carriages. This order was the largest single rolling-stock acquisition ever made in the United Kingdom.
Deployment commenced on the Metropolitan line in July 2010, followed by introduction on the Hammersmith & City line in July 2012, with full operation on the Circle and District lines achieved by September 2013. The replacement process concluded with the complete phase-out of A Stock on the Metropolitan line by September 2012; C Stock on both Circle and Hammersmith & City lines by February 2014; the Edgware Road branch of the District line by June 2014; and finally, D Stock on the District line by April 2017.
Overview
The letter S signifies suburban, consistent with the tradition of naming sub-surface London Underground trains after letters associated with their respective routes—such as A Stock on the Metropolitan line to Amersham, C Stock on the Circle line, and D Stock on the District line.
Belonging to Bombardier’s Movia series, this fleet consists of 192 trains: 133 seven-car S7 units operating on the Circle, District, and Hammersmith & City lines, alongside 59 eight-car S8 units dedicated to the Metropolitan line. This £1.5 billion investment stands as Britain’s most extensive single rolling-stock purchase.
The S Stock trains accelerate more rapidly than their predecessors at , reaching a maximum speed of , which is slightly lower than that of A Stock but exceeds that of C and D Stocks. During early operation phases, speed was limited to align with older train performance due to signalling system restrictions. The S8 variant accommodates 306 seated passengers—a reduction of 32% compared to A Stock—yet increases standing room by 25% (1,226 versus 976) and provides designated spaces for wheelchair users.
By 2017, reliability had improved significantly, with an average distance between failures around , representing a sevenfold increase over A and C Stocks and tripling that of D Stock. The power supply voltage was raised from 630 volts to 750 volts to support enhanced train performance, meet air-conditioning energy requirements, and enable regenerative braking capabilities.
Starting in 2016, these trains have been progressively outfitted with communications-based train control (CBTC) technology as part of the Four Lines Modernisation programme. This upgrade facilitates increased service frequency and reduced journey times. As of 2023, manual driving persists on most segments of the Metropolitan line and half of the District line, whereas fully automated operation is implemented across both Circle and Hammersmith & City lines.
Features
The S Stock trains are equipped with full air-conditioning, supported by the network's extensive open-air sections and sub-surface tunnels that help dissipate heat. Their regenerative braking system recovers approximately 20% of energy, feeding it back into the power supply to improve overall efficiency.
External destination and line indicators are displayed on the train’s outside, while larger internal dot matrix displays (DMIs) provide route information and safety notifications. The S8 Stock, operating on the Metropolitan line, also includes stopping pattern indicators and automated audio announcements. Unlike deep-level tube trains, these DMIs are mounted on the ceiling.
The air-conditioning units supplied by Mitsubishi feature dual circuits, ensuring that half capacity remains available if one circuit fails. Inter-car open gangways enhance passenger movement, increase standing room, and improve safety. CCTV cameras enable drivers to oversee all carriages, with video feeds showing the exterior of the train before departure. Driver cabs are fitted with fold-out steps to facilitate quick evacuation if necessary.
Seating is designed with cantilevered frames to simplify cleaning and provide space for luggage storage. Seating layouts vary: the S7 Stock, used on inner-city lines, consists entirely of longitudinal seats to maximize capacity during peak times; the S8 Stock, serving outer suburban routes, combines transverse and longitudinal seating arrangements and includes four wheelchair spaces per train. S7 trains have seven cars each, while S8 trains consist of eight cars.
Emergency alarm buttons located near wheelchair areas are protected by flaps to reduce accidental activations.
Although all S Stock trains can operate across the four sub-surface lines, S8 units are assigned exclusively to the Metropolitan line, whereas S7 trains serve the remaining three lines. Selective door operation is employed at stations with shorter platforms to manage passenger boarding effectively.
Design icon
As part of the Transported by Design initiative, on 15 October 2015, following a two-month public voting period, Londoners selected the walk-through S Stock train as one of the top 10 transport design icons.
History
Under the 2003 Public Private Partnership (PPP) for London Underground, Metronet was tasked with maintaining infrastructure on the District, Circle, Hammersmith & City, and Metropolitan lines. Bombardier Transportation, working within Metronet, was commissioned to design, manufacture, and service a fleet of 190 new trains: 40 for Circle and Hammersmith & City lines combined, 78 for the District line, and 72 for the Metropolitan line. These trains shared a unified design to minimize maintenance complexity and parts inventory but varied in length to accommodate different platform sizes. The first train was planned to enter service on the Metropolitan line by 2009, with full fleet deployment targeted for 2015.
In December 2006, Metronet and London Underground revealed the finalized train design featuring air-conditioning and walk-through carriages—both innovations for London Underground stock. An additional order comprising 40 cars valued at £105 million enabled seven-car formations on Circle and Hammersmith & City lines to match District line train lengths.
Metronet entered administration in July 2007 due to financial difficulties. After renegotiating Bombardier’s contract to continue delivery of new trains, Transport for London assumed control of Metronet’s responsibilities in May 2008. A public mockup of the new rolling stock was exhibited in September 2008.
Entry into service
Testing of the trains commenced in March 2009 at the Old Dalby Test Track located in Leicestershire, allowing trials to proceed without disrupting London line operations during weekends or evenings. The inaugural train was handed over to London Underground in October 2009. Manufactured at Bombardier’s Derby Litchurch Lane facility, production rates reached up to six trains weekly.
In 2015, TfL placed an order for one more S8 train intended for the Croxley Rail Link project, costing £15.5 million and increasing the fleet total to 192 units. The last train was delivered on 10 November 2016. However, the Metropolitan line extension project was cancelled in 2017.
Metropolitan line
Starting from November 2009, S8 Stock underwent overnight testing between and utilizing the Watford North Curve. Driver training programs began in January 2010, with the first train entering passenger service on 31 July 2010, operating between Wembley Park and Watford.
By June 2011, the S8 Stock had been deployed along the entire Metropolitan line. In November 2011, Transport for London paused further deliveries due to concerns over reliability; some units housed at Neasden Depot were temporarily withdrawn from operation. Deliveries recommenced by mid-December that year.
In August 2012, TfL announced plans to install strap handles following feedback from passengers regarding the height of handrails compared to those on A Stock trains.
By September 2012, all 58 S8 trains had arrived at Neasden Depot, leading to the complete retirement of the A Stock shortly thereafter. In November 2012, Bombardier was required to undertake urgent modifications on 37 trains at their own cost due to driver dissatisfaction with cab ergonomics. An additional S8 train was delivered as part of the now-cancelled Croxley Rail Link initiative.
During modifications and automatic train control (ATC) installation on S8 units, three extra eight-car trains called S7+1 operated on the Metropolitan Line. These consisted of a seven-car S7 formation with an added car but maintained all-longitudinal seating unlike S8s. By 2018, two of these were reverted to seven-car configurations and reassigned to the Circle, District, and Hammersmith & City Lines.
Hammersmith & City line
The initial introduction of S7 trains occurred on 6 July 2012 between Hammersmith and Moorgate. These seven-car trains measured , replacing the shorter six-car C69 and C77 models (), which necessitated platform lengthening at several stations. In locations where platform extension was unfeasible—such as —selective door opening is employed to prevent doors at the train’s ends from opening.
On 4 December 2012, an S7 unit underwent testing beyond Moorgate towards Barking during peak periods. Full deployment of S7 stock running from Hammersmith to Barking commenced on 9 December 2012, with complete operation by S7 trains achieved by 11 February 2014.
Circle line
S7 Stock began service on the Circle line on 2 September 2013, fully supplanting the aging C Stock fleet by 11 February 2014. The Circle line was prioritized for replacement due to its C Stock being in significantly poorer condition compared to the extensively refurbished District line D Stock completed between 2005 and 2008.
District line
Due to the comparatively newer D78 Stock fleet and recent refurbishment efforts, the District line was last to be fully converted to S7 Stock operation. The first S7 train operated between Olympia and West Ham starting on 2 September 2013.
Service expansion continued progressively: Wimbledon to Edgware Road from 6 February 2014; Ealing Broadway from 13 June; Richmond from 17 June; and Upminster from 16 January 2015. The phase-out of D78 Stock began on 19 January 2015. Bombardier finalized delivery of all 192 S stock trains by November 2016.
The last D78 unit was withdrawn on 21 April 2017, marking the District line’s complete transition to S7 Stock.
To enable operation over Network Rail-owned tracks between Gunnersbury and Richmond, as well as East Putney and Wimbledon, the S7 Stock was assigned the Class 499/5 classification under the TOPS system.
Automatic operation
Beginning in 2016, the Four Lines Modernisation initiative has transformed the four sub-surface lines to utilize automatic train operation through communications-based train control. This upgrade is designed to enhance service frequency and shorten travel times. The segment between Latimer Road and Hammersmith transitioned to automatic mode on 10 March 2019, followed by the deployment of additional phases known as Signal Migration Areas (SMA); by January 2023, six SMAs had been completed. However, due to financial constraints and technical complexities, automation efforts on the District line—which shares tracks with Network Rail and Piccadilly line services—have been reduced. As of 2023, the majority of Metropolitan line trains and roughly half of District line trains continue to operate manually, while Circle and Hammersmith & City lines run entirely on automatic control.
Accidents and incidents
- On 21 June 2020, an eight-car S8 Stock train on the Metropolitan line narrowly avoided a head-on collision with a Chiltern Railways two-car Class 165 diesel multiple unit at after the latter passed a danger signal. The two trains came to a halt only apart.
List of cars
Each vehicle is assigned a five-digit number: the second digit signifies the car category, while the final three digits denote the set number (ranging from 001–116 and 301–568). A-end cars carry odd numbers, whereas D-end cars have even numbers. Cars numbered 25nnn serve as replacements for 23nnn cars on trains equipped with de-icing systems.
| Set type | odd sets | A-end | D-end | even sets | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DM | M1 | M2 | MS | MS | M2 | M1 | DM | |||||
| S7 de-icer | 301–385 | 21nnn | 22nnn | 24nnn | — | 24nnn | 25nnn | 22nnn | 21nnn | 302–386 | ||
| S7 | 387–567 | 21nnn | 22nnn | 24nnn | — | 24nnn | 23nnn | 22nnn | 21nnn | 388–568 | ||
| S8 de-icer | 001–055 | 21nnn | 22nnn | 23nnn | 24nnn | — | 24nnn | 25nnn | 22nnn | 21nnn | 002–056 | |
| S8 | 057–115 | 21nnn | 22nnn | 23nnn | 24nnn | — | 24nnn | 23nnn | 22nnn | 21nnn | 058–116 | |
See also
- 2009 Stock, a deep-level train constructed by Bombardier Transportation for use on the Victoria line
- Movia, a series of metro trains manufactured by Bombardier Transportation