Some prototype steam powered railcars appeared in the mid 19th century and at the start of the 20th century over 100 were built. Diesel motors became powerful enough for a railway use after World War I and the Great Western Railway built several single cars and multiple units. A 1952 report recommended the trialling of lightweight diesel multiple units, followed by plans in the 1955 Modernisation Plan for up to 4,600 diesel railcars. Most of these had a mechanical transmission, but the Southern Region had experience of DC electric multiple units and diesel electric multiple units were introduced.