The Southern Railway created classification and numbering systems for its large fleet of electric multiple units, perpetuated by the Southern Region of

British Rail British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most of the overground rail transport in Great Britain from 1948 to 1997. It was formed from the nationalisation of the Big Four (British ra ...

until the early 1980s, when the impact of

TOPS Total Operations Processing System (TOPS) is a computer system for managing railway locomotives and rolling stock, known for many years of use in the United Kingdom. TOPS was originally developed between the Southern Pacific Railroad (SP), ...

was felt. Some stock is still allocated Southern-style classifications in a semi-official manner.

Classification

The early AC electric multiple units were referred to by a two-letter code. This was adapted for the DC third-rail system that was adopted by the Southern Railway, with units being given a three-letter code (sometimes two letters) prefixed by the number of cars in each unit, e.g. 4SUB for a four-car suburban unit. The Southern Region perpetuated this, and the same principles were adopted for diesel-electric multiple units but with single-letter codes. The last type to be officially allocated a designation in this series was the PEP stock of the early 1970s. Some types built since have been given semi-official designations in this style. ''This is different from the system used by British Rail (adopted from the LNER) to indicate the type of non-powered coach — see

British Rail coach type codes British Railways coach designations were a series of letter-codes used to identify different types of coaches, both passenger carrying and non-passenger carrying stock (NPCS). The code was generally painted on the end of the coach but non-gangway ...

.''

AC EMUs

DC EMUs

Diesel-electric multiple units

Unit numbering

Unit numbers were allocated from 1001, following the 1–1000 set numbers of semi-fixed formations of hauled coaching stock. Different types of unit were given numbers: This series was perpetuated by the Southern Region with modifications, as older set numbers were reused for the following different types: 2PEP reused number 2001, 4REP from 3001 and 4PEP 4001/4002. This series was abandoned in 1983, when units