At the end of the 1960s, British Railways adopted the Total Operations Processing System (TOPS), a computerised system developed by the Southern Pacific Railroad in the United States.
This page explains the first attempt at using TOPS and cross-refers the classes allocated with those adopted in the successful re-arrangement.
The first attempt to apply TOPS differed from the latter approach in two significant ways: The first attempt to apply TOPS to diesel multiple units saw each carriage within a unit being allocated its own unique class number.
Classes were allocated according to the following division: However, this arrangement was later revised so that each unit adopted the class number previously given just to the main type of Driving Motor car (the exception being the DEMU units, which were completely changed).
The table below cross-references the old and new TOPS classes: The first attempt to apply TOPS to the Southern Region's fleet of electric multiple units, saw classes being allocated according to the following division: In comparison with the later re-arrangement, the types that were different were given the same class (e.g. the single-car luggage vans) and identified only by subclass, while those that were later treated as variations of the same class, were separated according to their construction period (e.g. early or late 1950s builds).