British Rail Locomotive and Multiple Unit Numbering and Classification - 1948 Numbering and Classification - Modern Traction

Modern Traction

Numbering of electric multiple units was undertaken on a regional basis, with each region having its own series commencing from 001. Most diesel multiple units were not allocated unit numbers, though in later years numbers were allocated on a regional basis in the Scottish and Western regions, and by individual depots elsewhere. For more details on these series, see British Rail Regional Multiple Unit Numbering.

To classify electric stock, a two-letter prefix was used to indicate what type it was, followed by a number issued sequentially from 1. This was a system adapted from that used by the LNER for its electric stock (e.g. EM1, see here). The additional prefixes used were:

• AL: AC electric locomotive
• AM: AC electric multiple unit

The Eastern and North Eastern Regions used a series of different classifications for diesel locomotives. The first method was also adapted from the old LNER system, and applied only to diesel shunters operating on those regions. It comprised a prefix, indicating the transmission type and wheel arrangement, followed by a number allocated sequentially from 1. The prefixes used were:

• DEJ: Diesel-electric, 0-6-0 wheel arrangement
• DJ: Diesel-mechanical or hydraulic, 0-6-0 wheel arrangement
• DY: Diesel-mechanical or hydraulic, 0-4-0 wheel arrangement

The second classification system was developed in 1955 and applied to all types then in existence on British Rail. It was based on the format Dx/y, where x was the power of the locomotive in hundreds of horsepower and y was a number allocated sequentially to specific types (e.g. D1/1 would be a shunter with a 100 to 199 hp (75 to 148 kW) rating, D33/1 would be a Type 5 locomotive). The series was extensively re-arranged in 1962 in a somewhat confusing way, but following the same basic principles.

The Southern Region followed existing numbering (for its multiple units) and classification systems (for both multiple units and locomotives) inherited from the SR. The EMU classification system (e.g. 4SUB, see here) system was also extended to include their diesel-electric multiple units, but with a single letter. Locomotives were given a two-letter code, with the second letter indicating detail differences within the main type. For instance, what were to become Class 33 locomotives from 1973, were Class KA or KB depending on whether they were the standard design or that fitted for push-pull working with 4TC units.