electric lighting and upholstered seating in all classes. The City & South London Railway tube line opened in 1890, with electric locomotives which hauled three carriages. Originally only provided with small windows, these were soon nicknamed "padded cells". These were replaced with standard tube stock when the line was rebuilt in 1923. The Central London Railway briefly used carriages when it opened in 1900, but these were re-formed into multiple units in 1902–03. New carriages, nicknamed "Dreadnoughts", were introduced on the Metropolitan main line in 1910. Two rakes had a Pullman coach that provided a buffet service for a supplementary fare. They contained a toilet and were built with steam heating. Electric heating was fitted in 1925. All carriages on the London Underground were replaced by the A Stock multiple units in the early 1960s. Sub-surface electric multiple units Before 1933 the sub-surface lines were run by two companies, the District Railway and Metropolitan Railway. The Circle line was operated jointly, although the Metropolitan operated most of the services from 1926. District Railway In 1903, the District tested two seven-car trains with different control and brake systems on its unopened line between Ealing and South Harrow. Access to the car was by platforms with lattice gates at their ends and hand-operated sliding doors on the car sides. Later some trailer cars were fitted with driving controls, and two- and three-car trains operated from Mill Hill Park (now Acton Town) to Hounslow Town and South Harrow and later Uxbridge, until they were withdrawn in 1925. The District Railway ordered 60 × 7-car electric trains in 1903. A third of the vehicles were made in England, the rest in Belgium and France, and electrical equipment was installed on arrival at Ealing Common Works. Access was by sliding doors, double doors in the centre and single doors at either end. First- and third-class accommodation was provided in open saloons with electric lighting. The seats were covered with rattan in third class and plush in first. From 1906 the standard formation was six cars, with an equal number of motor and trailer cars running in either two- or four-car formations off-peak. By 1910 the District required additional rolling stock and ordered cars largely constructed of steel. The first batch arrived in 1911, followed by more in 1912 from a different manufacturer but to a similar design. Further cars arrived in 1914 with an elliptical