For electric service driving trailers and driving motors were planned. The First Class driving trailers were coded 'ACPD' for the sliding door stock.
There were only six cars coded 'ACPD'. These were: 1, 2, 8, 10 - 12. They were coded from _ACP_ cars 1920/1921.
In 1922, the electric traction codes were revised and the ACPD class was relettered to _D__.
Conversions after 1922 from ACP cars were coded directly to D.
Cars ACPD 1, 2 and 8 became D 201, 202 and 208. Cars ACPD 10, 11 and 12 were fitted with traction equipment and became _M__ sliding door motor cars numbers 244, 245 and 204.
The ACPD cars that became M cars were built with M car bodies and underframes already.