sentences:  From 1925 a sequential letter system was given that ran from A to M, although the M type never went into full production.This was replaced by a new series that used initials to describe the vehicle, such as 'RE' for 'rear engine'.Different chassis letter codes were used to identify different sizes of petrol engines, but with the introduction of diesel engines from 1933 the size and manufacturer was shown by a suffix to the main code.