Following conversion to air operated doors, the trains became collectively known as Q Stock.

Given that five different types of rolling stock were converted to Q Stock, the resulting hybrid trains looked bizarre - with the older carriages having flat sides and clerestory roofs, whilst the Q38 had flared sides at floor level.

The Q38 Stock, designed by LT's Chief Mechanical Engineer, William Graff-Baker, was built in 1939 for the District line by Gloucester RC&W to operate with the older, converted cars.

This was in connection with the conversion of Circle Line trains from five to six cars in length.

In the final years of service, Q Stock units were used on the East London Line, before withdrawal in 1971.