The 1920 Tube Stock consisted of forty cars built by Cammell Laird in Nottingham, England. These cars were the first new tube cars to be built with air operated doors. The batch consisted of twenty trailer and twenty control trailer cars, which were formed into six-car trains by the addition of twenty French motor cars built in 1906 and modified for air-door operation. They initially ran on the Piccadilly tube, but in 1930 were considered to be drab, compared to new stock being delivered at the time. The motor cars were therefore replaced by Standard Stock units, built in 1927, and the 1920 cars were refurbished. They were transferred to the Bakerloo line in 1932, and continued to operate until 1938.