Sub-Classes

Classes were introduced under the new Total Operation Processing System (TOPS) in 1972. Each Multiple Unit has a 6-digit number. Here's an example: 377301. The train is a 3-car Class 377 Electrostar, operated by Southern. As always, the sub-class is digit 4; 377301. Therefore, this is a Class 377/3. Beware! South Western Railway's Class 455 still retain their former Southern Region 4-digit unit numbers; e.g. (45)5701. In this case, the sub-class is the 2nd digit, here a 7. Sub-classes are important, and in this case, it denotes whether it is a 3-, 4- or 5-car train. In some cases, it also denotes what traction types it uses. If you only have the number of a unit, you can, in some cases, find out what livery it has. Later, I may add a feature where you enter the 6-digit unit number and it automatically tells you which category it comes under.