British Rail Class 378

The Class 378 Capitalstar is a type of electric multiple unit used on the London Overground network. The class is derived from the Class 376 trains currently used by Southeastern, and are also part of the Electrostar family, but featuring significant differences. Primarily, the Class 378 features fully longitudinal seating similar to that used on London Underground rolling stock, which is necessary for the high passenger volume services run on London Overground. The units were constructed by Bombardier Transportation, and were delivered in two separate batches.
The Class 378/0s were delivered as 3-car units with dual-voltage capability. They were extended to 4-car units in 2009–2010.
The Class 378/1s were delivered as 4-car units with third rail capability only. They are used on the East London Line and were previously used on the Watford DC Lines.
In 2014–16, all units had an extra carriage added to increase capacity, making them 5-car units. During the change, extended units carried a blue square on the front and back of the train saying "5 Car Train". These were taken off after all the trains were extended.