A major rebuilding of the main line from Wembley Park to Amersham was planned in the 1930s but delayed by the war. The line from Wembley to Harrow was rebuilt immediately after the war and the project was completed from 1956–1962, on a more modest scale than originally planned. Until 1961, passenger trains continued to be attached to a steam locomotive at to run to Aylesbury. The rebuilding electrified the line from Rickmansworth to Amersham, transferring all Aylesbury services to British Railways. A pair of fast lines was added from Harrow to north of Moor Park by 1962, allowing outer-suburban trains to run fast to Moor Park. Aluminium A stock, originally unpainted, replaced the T stock and locomotive-hauled trains. More A Stock trains were built in 1962–63 to replace the trains on the Uxbridge service, giving the main line a single train type for all services. A Stock was 4-car units that could operate as four- or eight-car trains; normally operated as eight cars, a 4-car unit operated the Chesham shuttle. One person operation of the trains was proposed in 1972, but due to conflict with the trades unions was not introduced on the line until 1986.