In 1932 the District Railway to Upminster had been electrified and new vehicles bought. Similar cars were ordered to allow the Metropolitan line be extended to Barking and replace some of the rapidly deteriorating original wooden trailers. The 1935–40 New Works Programme fitted electro-pneumatic brakes and air-operated doors to most of the District line stock, these becoming Q Stock and allowing the remaining wooden cars to be scrapped. A number of motor cars not suitable for conversion retained their hand-worked doors, and known as H Stock these ran until 1957. The joint Met and GWR stock on the Hammersmith & City line dating from 1905 was replaced by O stock that initially operated in 4 and 6-car formations, entering service from 1937. However, the train was entirely made of motor cars and this caused a problem with the electrical supply, so trailer cars were added from 1938. P Stock was ordered to replace all the remaining Metropolitan multiple units. A combination of 3-car units and 2-car units to run in six and eight car trains were delivered from July 1939. Two trailers were included in an eight car formation, but these were designed to allow conversion to motor cars at a later date after improvements to the power supply. After World War II, R Stock, composed of new cars and the Q Stock trailers that had been built in 1938, replaced the trains with hand-operated sliding doors that remained on the District line. The new trains were built between 1949 and 1959, and after 1952 trains were constructed from aluminium, saving weight. One train was left unpainted as an experiment and considered a success, so between 1963–68 trains were left unpainted or painted white or grey to match. A number of former District Railway F Stock became available for use on the Metropolitan line. These mainly worked the semi-fast Harrow and Uxbridge services, although they also ran on the East London line as modified four-car sets. This transfer allowed the Circle Stock to be replaced by 5-car trains of O and P Stock. After 1955, the traction control equipment was replaced on these trains and the cars relabelled CO and CP stock as appropriate. When the Amersham electrification project commenced in 1959, London Transport placed an order for 248 cars of A60 stock to replace the T stock and remaining locomotive hauled trains. A further twenty-seven trains of the A62