The CS class letters originate from 1939. In this year the Spirit of Progress cars and vans were given class letters and new numbers to enable new car construction. To this date ( 1937 - 1939 ) the cars were described in a general manner and the vans were unclassed and un-numbered.
The guards van listed as the 'Steel CE Van' became CS 1 in August 1939.
The baggage van listed as the 'Steel Bulk Mail' van became _DS_ 1 in 1939 too. DS 1 was fitted with a guards compartment and reclassed to CS 2 in 1956.
In 1962 when the 'Spirit of Progress' train was transferred from broad to standard gauge for through running, the carriage codes were again altered.
CS 1 and 2 were reclassed to VHN_ 1 and 2 during March 1962.