In the planning of the electrification project 1908 - 1914, the railways projected the use of about two hundred "excursion" cars. These carriages were to be used to provide special holiday passenger trains, daily "excursion" trips, and to supplement regular trains as required. There may also have been thinking about reducing the "holiday" car fleet: older cars that were only used for extra traffic occasions.
With the conversion of carriages to electric motors cars, surplus underframes could be re-used and a new design car body fitted.
The first car entered service in 1918. It was coded APL 1. The writer believes the underframe used was from the conversion of _BC_ 2 to ABCM 2, done in 1917.
There were eighty six cars built between 1918 and 1923.
The initial batch of APL cars were built with sliding doors. These were cars 1 - 26, 28 - 33. In country service the cars with these sliding doors were found to be very draughty. These cars were reclassed to BPL_ and more APL cars were built, this time with swing doors. Presumably APL 27 was the first car tried.
The new carriages were numbered 1 - 26, 28 - 33 to replace the first batch. Construction then continued on from No.34 and finished at No.54.
In 1928, APL 20 was converted for use as a railmotor trailer, probably a test car for trailers built for the PERM's.
In 1932/1933, fifteen APL cars were converted to Second Class and coded BPL. These cars were converted back to APL in the 1950's.
All remaining APL cars were converted to BPL in the 1960's.