S stock is the designation given to one train of eight cars by London Underground in the 1930s.

It was composed of converted trailers and experimental driving motor cars inherited from the Metropolitan Railway in 1933.

In 1919, the Metropolitan Railway converted six 1904 saloon stock cars into the "Hustler train".

In the London Passenger Transport Board numbering scheme, they became 2598 and 2599.

After the trailer cars were withdrawn from service in the 1940s, the two driving motor cars remained in service on the East London Line, being used with a 1923-built control trailer.