The 1920 Tube Stock consisted of forty cars built by Cammell Laird in Nottingham, England.

They initially ran on the Piccadilly tube, but in 1930 were considered to be drab, compared to new stock being delivered at the time.

A second planned refurbishment so that they could be used on the Northern City Line shuttle service between Moorgate and Finsbury Park stations was interrupted by the Second World War, and after hostilities ceased, 35 of the cars were scrapped.

This was a government initiative to fund projects which would create employment in the aftermath of the First World War, and enabled the Treasury to inject £5 million into the Underground.

In order to ensure that the opening was 6 feet (1.829 m) tall, the top of the door curved inwards, following the roof line.

However, this proved to be too sensitive, and in order to maintain the advantage of shorter times at stations, was disabled after an initial trial period.

When the train was ready to depart, the valve was de-energised, admitting air to the large cylinder, and the door closed.

The remaining 18 cars were adapted by Gloucester Railway Carriage and Wagon Company, with the final one completed in June 1924.

There were differences in the implementation of the conversion, as the railway company was considering a plan to convert all of the gate stock cars to air-door operation, and this small batch provided an opportunity to experiment with what might be possible.

Changes were made to the couplers between the cars, and the air-doors on the driving cabs of the control trailers were replaced by swing doors.

[12] At the time, the Piccadilly line was being extended, with the extensions involving open-air running, and the 1920 stock was unsuitable for use in wet conditions.

It was intended to recondition them, and use them on the Northern City Line shuttle from Moorgate to Finsbury Park, but the onset of the Second World War prevented that, and they were stored at Cockfosters Depot.