The order was for a total of 192 trains (1,403 cars), and consisted of two types, S7 Stock for the Circle, District and Hammersmith & City lines, and S8 Stock for the Metropolitan line, with differences in the arrangement of seating and number of cars.

[3] From 2016, the fleet has been converted to use communications-based train control (CBTC) as part of the Four Lines Modernisation.

The DMIs show destination and line, and can display other messages such as safety notices.

There are also DMIs on the exterior, with text alternating between destination and line, and on S8 Stock the stopping pattern (fast, semi-fast or all stations).

The S8 Stock is the first on the Metropolitan line with dot-matrix indicators and automated voice announcements.

The air-conditioning system, the first on London Underground trains, is supplied by Mitsubishi and has two circuits so that if one fails there is still 50% capacity.

[20] The S stock has cantilevered seating for easy cleaning and accessible storage of bags.

[23][24] Following the implementation of the London Underground Public Private Partnership (PPP) in 2003, the Metronet consortium became responsible for the infrastructure on the District, Circle, Hammersmith & City and Metropolitan lines.

[25] As part of the consortium, Bombardier Transportation would design, build and maintain new trains for these lines.

[28] In July 2007, Metronet, the private consortium responsible for the infrastructure for the sub-surfaces lines, collapsed due to financial difficulties.

[34] Built at Bombardier's Derby Litchurch Lane Works, trains were constructed at a rate of six a week at the height of production.

A number of trains were delivered to London Underground's Neasden Depot, but were not accepted to enter service.

[41] An additional S8 train was later delivered, as part of the subsequently cancelled Croxley Rail Link project.

S7 Stock began operating a full service from Hammersmith to Barking on 9 December 2012.

The first S7 Stock train entered passenger service on the line between Olympia and West Ham on 2 September 2013.

In November 2016, the last of 192 S stock trains were completed by Bombardier and handed over to London Underground.

[1][46] The D78 Stock was completely replaced by the S7 with the withdrawal of the final unit from service on 21 April 2017.

[47] The S7 Stock received the Class 499/5 designation on the TOPS system in order to operate on the District line between Gunnersbury and Richmond, and between East Putney and Wimbledon, as these track sections are owned by Network Rail.

[15][16] The section between Latimer Road and Hammersmith was the first to be switched over to automatic operation on 10 March 2019,[48] with further extensions being implemented in stages called Signal Migration Areas (SMA); as of January 2023 the first six SMA areas have been implemented.