Until the mid-1950s, the SNCV owned the infrastructure and rolling stock of the coastal tram lines, but the operation was outsourced to SELVOP, founded in 1927. The trams often consisted of a motor vehicle of the 'Standard Coast' type, several closed and open trailers and sometimes a freight wagon. This equipment, often with wooden or rattan benches, was outdated and had to be replaced.
From 1953 onwards, new 'S' type motorcars were built for other electrified networks, but investment in the coastal trams was postponed until after the expiry of the SELVOP concession on 1 January 1956. After this date, the SNCV built 28 new 'SO' type motorcars in a year and a half, using parts from older motorcars.
The new motor cars had a more luxurious interior with 34 seats instead of the 40 of their predecessors. They were equipped with more modern amenities such as electric doors and a more attractive design, which made for an improved travel experience. In the 1960s and 1970s, the markings on the doors were updated for clarity. Passengers could move through the motor car from the back to the front, with a receiver at the rear.