The A Stock cars were built for the Metropolitan District Railway by Brush Traction in 1903. They were the prototype electric units tested by the Metropolitan District Railway. Of the total of fourteen cars, four were End Driving Motors, located at the ends of each unit, two were Middle Driving Motors, located in the middle of the unit, and eight were trailers. Later, two of the trailers were rebuilt into Control Trailers. These units were wooden-bodied and led to the development of the B Stock. The last car was withdrawn in 1925 and no examples passed to the London Passenger Transport Board.