Editing TOPS (section)

==Adoption by British Rail==
During the late 1960s, [[British Rail]] (BR) was looking for ways to increase efficiency, particularly of its declining freight operations, and identified a computer-based system as a key tool for improving both planning and control.<ref name = "railarch"/> The specific requirements included the more effective utilisation of freight rolling stock, better pre-planning of terminal and marshalling yard operations, better alignment of specific consignments to specific services, prompt response to customer location-related requests. BR planners realised early on that it would be quicker and cheaper to buy an existing system, rather than develop one locally, even if that breached the [[Government of the United Kingdom|British Government]]'s requirement for nationalised industries to '[[I'm Backing Britain|Buy British]]'.

Various systems around the world were explored, such as France's Gestion Centralisée du Trafic Marchandises (GCTM) and Canada's Traffic Reporting and Control System (TRACS), but found this to be ill-suited to BR's requirements; in fact, no existing system in the world satisfied them in full.<ref name = "railarch"/> However, SP's TOPS system met many - but not all - of the outstanding requirements. Starting in June 1970, several delegations from SP came to the UK to discuss and evaluate BR's existing practices, along with corresponding visits to the USA to witness SP's operations, before both sides concluded that TOPS was a viable option.<ref name = "railarch"/>

Groundwork on TOPS' financial case had commenced in the summer of 1970, during which a four-year timescale for implementation had emerged as the preferred option.<ref name = "railarch"/> From an analysis performed in 1971, it was found that, even in the event of the most pessimistic assumptions being true, TOPS' introduction retained a healthy gain in net value of £34m per annum. Suitably convinced of its benefits, BR's board opted to purchase the system, along with the source code (as was typical in those days for such a large mainframe-based system) during June 1971.<ref name = "railarch"/> Due to its foreign origins, the purchase of an [[IBM System/360]] mainframe to operate TOPS had to be approved by the [[Heath ministry|Heath cabinet]], which was given in October 1971. The decision was justified by a belief that TOPS would enable BR's freight operations to become profitable.<ref name = "railarch"/>

The cost of BR's TOPS implementation included £5.6m of capital costs, development costs of £5.7m, and equipment rental costs of £22.5m between 1972 and 1980.<ref name = "railarch"/> Aside from the computers themselves, and suitably trained staff to operate them, perhaps the most technically challenging aspect impacting implementation was [[telecommunications]], necessary to bring the system's geographically disparate elements together.<ref name = "railarch"/> The implementation phase was greatly assisted by data processing experts provided by SP. It was at the urging of SP's specialists that BR omitted the originally-sought volume acceptance feature, as it was considered to be impractical.<ref name = "railarch"/>

The operational headquarters for TOPS was established in an existing railway office block in close proximity to BR's corporate headquarters.<ref name = "railarch"/> The building had to be extensively refitted for the scheme, the top floor being turned into an open-plan office for housing planning and development work, while the computing equipment and telecommunications gear was accommodated across two separate floors below; the latter requiring a controlled climate for reliable operation. According to Amott, the implementation of TOPS was undertaken without any significant adverse reaction in terms of [[trade union|industrial relations]] or senior management.<ref name = "railarch"/>

The adoption of the TOPS system during the early 1970s led to several changes in working practices across Britain's railway network. Hitherto, locomotives had been numbered in three different series. [[Steam locomotives of British Railways|Steam locomotives]] carried unadorned numbers up to five digits long. [[Diesel locomotive]]s carried one to four-digit numbers prefixed with a letter 'D', and electric locomotives with a letter 'E'. Thus, up to three locomotives could carry the same number. TOPS could not handle that, and it also required similar locomotives to be numbered in a consecutive series in terms of classification, so that they might be treated as a group.

===TOPS numbering under British Rail===
{{Details|British Rail locomotive and multiple unit numbering and classification#1973 numbering and classification - TOPS|British carriage and wagon numbering and classification}}
[[File:British Rail Class 31-4 dataplate.jpg|thumb|''Brush Type 2'' locomotives became [[British Rail Class 31|Class 31]] under TOPS. This is the data panel from a Class 31/4; the 31/4 subclass being used for locomotives with [[Electric Train Heating]].]]

Sequentiality was all that was required but, given the need to renumber, it was decided to adopt a logical system for classification, and the five- or six-digit TOPS number was divided into two parts. No class of locomotive or [[multiple unit]] numbered over 1,000 examples, so the last three digits were used for the individual number between 001 and 999 in that class, although [[British Rail Class 43 (HST)| Class 43]] goes down to 000, that being the number of the only remaining [[British Rail Class 41 (HST)|HST prototype]] power car. The first two or three digits were used to denote the class of locomotive or multiple unit. The numbers were often written in two space separated groups, such as "47 401" to highlight that division, but the TOPS system actually stored and displayed them without the space: "47401". Sub-classifications were indicated in the TOPS system with a slash and a subclass number, e.g. "47/4". It was convention, though not enforced within the TOPS system, that subclass numbers were boundaries in the locomotive numbering system, such that class "47/4" started with number "47 401". If there were more than 99 numbers in a subclass, the number series extended to the next value of the third digit; thus, since there were more than 200 locomotives in class "47/4", subclasses "47/5" and "47/6" did not exist, and the next valid subclass by convention was "47/7" starting with "47 701".  However, in some cases, the sequences do not match, e.g. [[British Rail Class 158|158/'''0''']] numbers start at 158 '''7'''01.

Locomotives are assigned classes 01–98: diesel locomotives 01–79 (originally 01–69), AC electric locomotives 80–96, departmental locos (those not in revenue-earning use) 97, and steam locomotives 98. DC [[electric locomotive]]s were originally allocated classes 70–79 but this was modified in 2011 (see [[British Rail locomotive and multiple unit numbering and classification]]); the sole relic of this is [[British Rail Class 73|Class 73]] which continues unrenumbered, probably because it can be considered equally a diesel locomotive as it is a DC electric. One oddity was the inclusion of British Rail's shipping fleet in the system as Class 99. [[Diesel multiple unit]]s (DMUs) with mechanical or hydraulic transmission are classified 100–199, with electric transmission 200–299. [[Electric multiple unit]]s (EMUs) are given the subsequent classes; 300–399 are overhead AC units (including AC/DC dual-voltage units), while Southern Region DC [[third rail]] EMUs are 400–499, other DC EMUs 500–599. More recently, new electric multiple units and [[Electro-diesel multiple unit|bi-mode multiple units]] have been given the 700 series and new [[High-speed rail|high-speed]] units have been given the 800 series. Selected numbers in the 900 series have been used for departmental multiple units, mostly converted from former passenger units.  

[[Coach (rail)|Coaching stock]] and individual multiple unit cars are allocated five-digit numbers; since the early 1980s, it has been forbidden for them to have the same numbers as locomotives, but before then duplication was possible because they carried a prefix letter, which was considered part of the number. More recent EMU deliveries have six-figure coach numbers.