|Historical notes: ||The majority of the large Sydney suburban rail network was electrified between 1926 and 1929, with modest additions taking place during the 1932 - 1939 period. In 1950, it was decided to electrify the difficult double-track section of line over the Blue Mountains to the west of Sydney. The line to Penrith was electrified in 1954/55, allowing suburban electric trains to serve this route. To cater for this added growth and also to accommodate future expansion, a need for additional cars was realised. Accordingly, a contract was placed with the Commonwealth Engineering Co. of Granville for 80 steel suburban cars (40 motor and 40 matching trailers). In addition, this company also received a contract for a similar number of stainless steel "inter-urban" cars to provide services over the Blue Mountains when that line was eventually electrified to Lithgow in 1957. Because their introduction to service coincided with the launch of Russia's Sputnik craft into space, the new trains, because of their "S" targets, quickly acquired the name "Sputnik Sets", a term they retained until withdrawal.
In the 1960s, tenders were called for double deck electric passenger cars. In February 1964, the local Sydney engineering firm of Tulloch Limited delivered the first of 120 double-decker trailer cars for use in Sydney. These cars, constructed of riveted aluminium on a steel underframe and riding on bogies featuring air bag suspension, were actually lighter than the steel trailer cars then in service. The first 40 of these double-deckers, T4801 to T4840, replaced the 40 trailer cars (T4701 to T4740) in the Sputnik Sets. Accordingly, when built, T4801 to T4840 were equipped with power-operated doors, had Sputnik set compatible lighting and control voltage and Sputnik set compatible jumper coupling receptacles. They consisted of a normal floor level over the bogies, with a double deck passenger section between the bogies. They carried green internal livery and were painted Tuscan Red on the outside sides with painted silver roofs to match the single deck carriages. For the first time in Sydney, fluorescent internal lighting and air suspension bogies were used. The initial 40 cars were used in power door sets, the remainder in non-powered door sets, and they replaced the remaining wooden bodied trailer cars.
In 1968, an experimental all double decker electric train was produced by Tulloch Limited, based on their double deck trailer design, and it was designated set S10. In 1972, complete 8-car double decker production trains began entering service in Sydney. They initially carried the "targets" S11 onwards. However, to save confusion, the "Sputnik" sets carrying the targets "S" were re-designated "W".
The W set trailers (T4801-4833) and M set trailers (T4834-4838 & 4896-4920) remained in service until November 1993 when the last 8-car set was withdrawn, replaced by a new Tangara 8-car double deck set. the cars marshalled with Comeng power cars in R/S sets saw service until 2003 when the introduction of the Millennium Trains saw their final retirement. Cars 4801, 4814, 4854 & 4874 have been retained as heritage cars.