[3] The trains featured longer cars and larger door space than the previous units, being designed for airport travellers with luggage.

There are also 21 double-ended units, formed DM-T-DM, to provide additional flexibility and to operate the Aldwych shuttle (now closed).

[7] The interior was completely remodelled, with changes including the removal of transverse seating, replacement of the original wooden flooring with new floor material, replacement of straphangers with new grab rails, new enclosures for the ceiling ventilation fans, brighter lighting with new diffusers, installation of car-end windows and new perch seats in the centre of the cars, creating more luggage space for airport passengers.

[7] The original unpainted exterior was painted in London Underground's corporate livery, and a new emergency detrainment system was fitted in the cabs.

The EVO tube concept design, a lighter articulated train with walk-through cars, was introduced early in 2011.

[14] The ASLEF and RMT trade unions that represent the drivers strongly oppose this, saying it would be unsafe.