British Rail TOPS First Arrangement - Locomotives

Locomotives

The first attempt to apply TOPS differed from the later approach in two significant ways:

• xx/0 was not a valid sub-class number. When the second arrangement was applied original subclasses xx/1 became xx/0, xx/2 became xx/1 and so on.
• Some detail differences within classes were considered sufficient for a different class number to be allocated, rather than indicate it with a sub-class. In addition, there are a number of cases where conversions led to complete reclassification, where similar circumstances later would be indicated simply by allocating a new subclass. The change in approach led to some odd gaps in the list of locomotive classes when they were re-arranged as the principal class numbers were retained unaltered. Classes affected by this change in approach include:
  • Class 29 (re-engined Class 21)
  • Class 31 (re-engined Class 30)
  • Class 34 (became Class 33/1)
  • Class 43 (North British Locomotive-built Class 42)
  • Class 48 (Class 47 with experimental engine)
  • Class 72 (became Class 73/0)