The T Stock was a series of electric trains originally built in various batches by Metropolitan-Vickers and the Birmingham Railway Carriage and Wagon Company for the Metropolitan Railway in 1927–31 for use on electric services from Baker Street and the City to Watford and Rickmansworth, though rarely some worked on the Uxbridge branch.

As built, the group has some variations in equipment, mostly to allow use with existing stock such as the Saloon and Ashbury trailers[clarify] and leading to incompatibilities within the class, however upon transfer to London Transport this was rectified and the entire fleet largely standardized about 1938.

These electric multiple unit trains had slam doors with rounded tops, thought to be less prone to damage if accidentally opened in the tunnels north of Baker Street.

This batch included specially built trailers and when running with which were known as 'MW' trains; the W indicating Westinghouse Air Brakes were fitted.

They were found not to be as compatible as hoped, and remained segregated until the London Passenger Transport Board (LPTB) standardisation of Metropolitan Railway rolling stock.