For the electrification project, steam hauled _AP_ trailer cars were fitted with electric equipment and reclassed APT with the existing AP numbers retained.
The conversions took place between 1919 and 1921. The APT numbers ex AP cars were 1 - 26, 28 - 30, 32, 37, 41, 45, 46 - 50 and 57.
In June/July of 1921, four ACP_ carriages were also recoded to APT. ACP 25 to APT 63, ACP 26 to APT 64, ACP 27 to APT 65, ACP 42 to APT 80. The ACP carriages were a First Class carriage with a guards van compartment.
The ACP to APT cars were "Ringer" cars, a practice initiated in 1912 with guards compartments stripped of emergency equipment ( handbrake, emergency brake tap ) and fitted with passenger seating. The van doors were painted with a large white circle to indicate to train crews 'No Emergency Equipment'.
Between 1921 and 1923 the APT class was rationalised to class _T__. The carriages were renumbered by adding '200' to the existing number. Eg APT 20 to T 220.