Gaps in the locomotive class numbering scheme.

Gloster said:

All five D600s were withdrawn on 31 December 1967. I can’t see BR keeping a class open just in case some preservationists might use it

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mods note - split from this thread

There has been much debate about the reason for some class numbers not having been used when they were first publicised in 1968. Why no 18, 19, 32, 34, 36, 38, 39, 41, 49, 51, 53 or 54? It has been suggested in some circles that, like the non-use of Class 72 (as originally published) for what became 73/0, a number of the original proposed classes were subsumed into bigger classes (eg 17, 18 19 all became 17), and others became extinct

Do we know when the first internal draft of the list of classes was compiled? If it was in 1967, the D600s (aka D20/4) would have been allocated a class.

various exotica are listed here as still extant in early 1967, many of which could have filled the gaps in the list eventually published


Incidentally, although the introduction of TOPS has often been cited as having been the reason for introducing the new classification system (the latest of several used by BR in the 50s and 60s), the proposal to computerise the frieight management process was not made until 1970, and the choice of TOPS was not made until 1971, three years after the classification system was introduced.


However, it was the adoption of TOPS that necessitated the actual renumbering, as the system couldn't be adapted to cope with D and E prefixes

norbitonflyer said:

There has been much debate about the reason for some class numbers not having been used when they were first publicised in 1968. Why no 18, 19, 32, 34, 36, 38, 39, 41, 49, 51, 53 or 54? It has been suggested in some circles that, like the non-use of Class 72 (as originally published) for what became 73/0, a number of the original proposed classes were subsumed into bigger classes (eg 17, 18 19 all became 17), and others became extinct

Do we know when the first internal draft of the list of classes was compiled? If it was in 1967, the D600s (aka D20/4) would have been allocated a class.

various exotica are listed here as still extant in early 1967, many of which could have filled the gaps in the list eventually published

But i fear we are getting off-topic

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I believe that it was introduced internally in 1968, although when in 1968 I know not. So it is quite possible that the D600s were allocated Class 41 while the system was being prepared, but this was struck from the list by the time it was formally approved as no longer relevant.

I have always thought that the missing 32, 34, 51, etc. was simply because there were so few types in the Types 3 and 5 that gaps were left so that any new types could be fitted in as best suited their power.

There was a Class 53, at least semi-officially. D0280 was bought from Brush in 1970 to become 1200, but I don’t think it ever carried 53 001 before withdrawal in 1975.

This has always fascinated me, and I dream up all sorts of theories. In terms of timing, I think there are some clues: Classes 30 and 31 were used for the Brush Type 2s, so it was before completion of the re-engining programme. And Classes 21 and 29 were used for the NBL Type 2s, so it was after the start of their rebuilds. But the best clue to the actual date of compilation presumably comes from which shunters got class numbers and which didn't? Of the obscure classes, only 10, 11 and 12 were used: 10 = Lister/GEC version of the 08, but the Lister/BTH version didn't get a class number; 11 = LMS predecessor of the 08, but some of the earlier versions didn't get class numbers; 12 = SR predecessor of the 08, but again earlier variants didn't get a class number. The GWR and LNER predecessors of the 08 also didn't get class numbers. Somewhere in that there's some clues if I could just work it out!

re "class 41" for D600, no-one and I mean no-one, in 30 years of me asking this question, and searching myself, has ever been able to produce any official BR document of any date that refers to them as such.

To my knowledge and memory, no one, official or unofficial, ever used "class 41" for D600s until CJMarsden produced /his/ list c.1980 or so. And that was not based on a BR list (he told me that himself some years ago). Since then, the whole thing has been plagiarised.

Right up to 1968, all WR operating information then used the term D6XX as in D10XX D8XX D70XX following on from kettle classes like 28XX 43XX and so on.

The same applies to "class 80" for E2001 - no-one can produce any BR document with this in.

Fleetwood Boy said:

But the best clue to the actual date of compilation presumably comes from which shunters got class numbers and which didn't? Of the obscure classes, only 10, 11 and 12 were used: 10 = Lister/GEC version of the 08, but the Lister/BTH version didn't get a class number; 11 = LMS predecessor of the 08, but some of the earlier versions didn't get class numbers; 12 = SR predecessor of the 08, but again earlier variants didn't get a class number. The GWR and LNER predecessors of the 08 also didn't get class numbers. Somewhere in that there's some clues if I could just work it out!

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Of the shunter classes, the only ones to get class numbers but to have no examples renumbered were 04, 10, 11, 12 (and 14 if they count).

The sources I have give the year (but not the month) of withdrawal of the classes of interest, and nearly all were in 1967. The exceptions are

1968
NBL/Paxman 0-4-0 (D2700 class)
NBL/MAN 0-4-0 (D2708 class)
Ruston 0-4-0 (D2957 class)

1969
Barclay/Gardner 0-6-0 (D2400 class) - it is possible these were intended to be classed together with their 0-4-0 cousins as Class 06, despite the different wheel arrangement (which gave them RA2 instead of RA6 !)

This suggests that the list was drawn up some time in 1968, after the NBL and Ruston types were withdrawn, as they were too disimilar to any surviving types to have shared a classification with them. And the D600s had indeed been withdrawn by then.

So what were the gaps for? There seems to be no pattern to them being simply providing room for new classes as yet unplanned (only two missing between 01 and 31, but then five missing in the thirties, and just two in the forties (where expansion was perhaps most likely). So it seems plausible that the gaps were for varianst that were later decided to be lumped together, but there was no need to alter the rest of the list.
Even so, there are oddities - a difference in engine rating was enough to distinguish a 24 from a 25, or a 44 from a 45, but class 17 included two examples with a completely different make of engine from the rest. Similarly, there were four different varaitions in electrical equipment within Class 25, and yet a difference in electrical equiopment was all that distinguished classes 45 and 46

Were 18 and 19 originally intended to cover the variants of class 17 with different coupling codes and engines)
Was a class number in the 30s kept for the Brush Type 2s with uprated (1600hp) Mirrlees engines (at least one of which was still extant in 1967)?
Were the Hastings 33s originally to be a different class? and/or the Push Pull ones?
There was, I understand, a difference between the first 119 class 37s and the rest - hence the renumbering of D6700 as 37119, and 37119 as 37308 37283. Could that account dfor another gap?
Could class 41 have been intended for D800-802, which differed from the standard class 42, and were not withdrawn until 1968?
There were numerous variants amongst the Brush Type 4s in the late 1960s - as well as the V-form engines (class 48), there were the first twenty ("Generators"), and the various uprating and downrating of engines. Could they account for the missing classes 49, 51, 53 and 54? (53 was later used for the Falcon prototype when it was taken into BR stock, although it was withdrawn before getting a five digit number)

It is probably impossible now to identify the staff responsible for drawing up the list nearly sixty years ago, even if they are still with us, so unless an early draft emerges from the archives, we will probably never know.

norbitonflyer said:

There was, I understand, a difference between the first 119 class 37s and the rest - hence the renumbering of D6700 as 37119, and 37119 as 37308. Could that account dfor another gap?

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I think 37119 was the first to have a centre headcode box rather than split boxes and access doors, so this would neatly avoid a 37000 and keep the body types in neat groups. Was anything else changed apart from the doors and boxes?

SuspectUsual said:

I think 37119 was the first to have a centre headcode box rather than split boxes and access doors, so this would neatly avoid a 37000 and keep the body types in neat groups. Was anything else changed apart from the doors and boxes?

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Not quite. D6819 was the first to have central headcode boxes....and that was renumbered 37 283 under the TOPS scheme, taking the place of D6983, which was destroyed in the Bridgend collision. First of class D6700 was renumbered 37 119 under TOPS - to keep the similar locos together - and therefore 37 120 was the lowest-numbered loco with central headcodes under TOPS.

D6130 said:

Not quite. D6819 was the first to have central headcode boxes....and that was renumbered 37 283 under the TOPS scheme, taking the place of D6983, which was destroyed in the Bridgend collision. First of class D6700 was renumbered 37 119 under TOPS - to keep the similar locos together - and therefore 37 120 was the lowest-numbered loco with central headcodes under TOPS.

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Ah right, that makes sense, and I do have a vague recollection of an accident withdrawal. And to think I'd tell people one of my strengths is that I'm good with numbers!!

norbitonflyer said:

Of the shunter classes, the only ones to get class numbers but to have no examples renumbered were 04, 10, 11, 12 (and 14 if they count).

The sources I have give the year (but not the month) of withdrawal of the classes of interest, and nearly all were in 1967. The exceptions are

1968
NBL/Paxman 0-4-0 (D2700 class)
NBL/MAN 0-4-0 (D2708 class)
Ruston 0-4-0 (D2957 class)

1969
Barclay/Gardner 0-6-0 (D2400 class) - it is possible these were intended to be classed together with their 0-4-0 cousins as Class 06, despite the different wheel arrangement (which gave them RA2 instead of RA6 !)

This suggests that the list was drawn up some time in 1968, after the NBL and Ruston types were withdrawn, as they were too disimilar to any surviving types to have shared a classification with them. And the D600s had indeed been withdrawn by then.

So what were the gaps for? There seems to be no pattern to them being simply providing room for new classes as yet unplanned (only two missing between 01 and 31, but then five missing in the thirties, and just two in the forties (where expansion was perhaps most likely). So it seems plausible that the gaps were for varianst that were later decided to be lumped together, but there was no need to alter the rest of the list.
Even so, there are oddities - a difference in engine rating was enough to distinguish a 24 from a 25, or a 44 from a 45, but class 17 included two examples with a completely different make of engine from the rest. Similarly, there were four different varaitions in electrical equipment within Class 25, and yet a difference in electrical equiopment was all that distinguished classes 45 and 46

Were 18 and 19 originally intended to cover the variants of class 17 with different coupling codes and engines)
Was a class number in the 30s kept for the Brush Type 2s with uprated (1600hp) Mirrlees engines (at least one of which was still extant in 1967)?
Were the Hastings 33s originally to be a different class? and/or the Push Pull ones?
There was, I understand, a difference between the first 119 class 37s and the rest - hence the renumbering of D6700 as 37119, and 37119 as 37308. Could that account dfor another gap?
Could class 41 have been intended for D800-802, which differed from the standard class 42, and were not withdrawn until 1968?
There were numerous variants amongst the Brush Type 4s in the late 1960s - as well as the V-form engines (class 48), there were the first twenty ("Generators"), and the various uprating and downrating of engines. Could they account for the missing classes 49, 51, 53 and 54? (53 was later used for the Falcon prototype when it was taken into BR stock, although it was withdrawn before getting a five digit number)

It is probably impossible now to identify the staff responsible for drawing up the list nearly sixty years ago, even if they are still with us, so unless an early draft emerges from the archives, we will probably never know.

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Interesting. When did it become the practice to utilise subclasses (eg 47/0) i wonder? Perhaps the original intention was to have separate classes but then it was realised using subclasses was a neater way of dealing with minor variations? Although I’ve always wondered about the logic of the subclasses - for example, a 47/0 turning up to work an eth set wouldn’t be a terminal problem, but a vac only 47 turning up to work air braked set would be.

Fleetwood Boy said:

Although I’ve always wondered about the logic of the subclasses - for example, a 47/0 turning up to work an eth set wouldn’t be a terminal problem, but a vac only 47 turning up to work air braked set would be.

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47s were all DB very early on and had been done by the time I was training in 1978.

Other classes with mixed VB and DB (and mixed heat arrangements) got allocated to compatible jobs by sheds/controllers, although I often wondered about the 56 sent to New Street to drag a roarer and VB adex set. It got to Nuneaton OK and luckily the roarer’s batteries held out long enough to translate!

norbitonflyer said:

Could class 41 have been intended for D800-802, which differed from the standard class 42,

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That is my theory too. And I stress theory. No evidence. Or D830 was 41, and D800-802 maybe 38 or 39.

Same for 17s I think the 3 sub classes might have been 17 18 19 as they were all a bit different.

I always say in this debate that one must stand back from the OCD trainspotter trait of everything must have a class / list must have no gaps / everything has a place holder / everything is done with logic.

And don't try work any of it out backwards from any unofficial publication like contemporary IA ABC spotting books, for apart from anything else they are flawed and do not contain all the needed data.

However the final published list came about, it did not suddenly go from non existence on Day -1, written on Day 0, and into use on Day 1. There would have been a gestation period through central BR HQ and all the regional offices.

My theory is this. Well 2 theories. The first theory is forget the ER diesel classification list that IMHO has SFA to do with it.

The second theory is the key document is the BR Diagram Book. If you can get hold of one of these pre-1968 classes, you find in order Types 1 2 3 4, prefixed DH or DE, and the go something like DE/1001, DE/1002, DE/1003 for the first three d-e Types 1 (there is no need to list the actual types here I am showing a concept), then Type 2s DH/2001 DH/2002 DE/2001 DE/2002 etc etc. In the order in the book DH of one Type always precedes DE, while within each DH and DE block they are more or less but not exactly in crankshaft hp order. I have a 1966 copy, complete except for some reason all the 'peaks' are missing (it looks like someone had ripped them out).

My theory is that the new classes were not a complexicated calculation worked out by high ranking BR officers, but the upper food chain commanded and it got cascaded to someone - possibly even an apprentice - it is the kind of task that would be delegated that far down - in the Derby drawing office to get out a current Diagram Book, start at 01, and keep going. No gaps. This list would then be reviewed by command at higher HQ and regional levels who filtered out some of the unecessary demarcation your drawing office bod would have been oblivious too. Remember, we are experts at all the sub types - a non crank in a office doing a tedious task is not.

This review, that almost certainly had more than one iteration, knocked out some numbers by combining that which was split (e.g. my theory that 17s might have been 17 18 19 in a first list then commen sense took over), and, also, key point, is while all this was going on some classes were eliminated. The solution is to find the exact dated BR Diagram Book that was used - and no it was almost certainly not that of one day before the final new class list was released.

This entire debate has been going on and on for decades, it comes up time and time again over the years, there is no single answer been found for it, and people have theories and counter theories as to why X become Y and not Z and how or why Q is missing. None of this helped by people repeatedly regurgating lists that contain incorrect info like D600s and E2001.

Just some musings.......pure conjecture but to some extent the missing numbers may have worked something like this?

18 - was this originally the one-off DHP1 "Super Clayton" which I don't think ever ran on BR?
30 - Brush type 2 with original engines. But what about the uprated ones?
32 - Has been claimed to be on the original draft of TOPS for the Hastings class 33
34 - Known to have been originally intended the pushpull class 33
36 - 10000 / 10001 precursor to the 37, slightly less power than 37 so closest lower number
38 - 10201 / 10202 precursor to the 40, but lower power (type 3)
39 - 10203 revised uprated type 4 precursor to the 40. Different class as different power output
41 - D6XX ?
49 - DP2 prototype for the 50s so given one number less?
51 - Lion? Its Sulzer engine was never downrated which may have resulted in a higher class number than the 47?
54 - Wasn't this intended for the "SuperDeltic"?

Queries
10800 - as the prototype for classes 15 & 16 this should have logically been class 14. However did the rebuild by Brush with a 1400hp Maybach mean this was changed? (And of course 14 was used for the Swindon type 1)
10100 - the Fell loco. Would have been in the type 4 range, but scrapped too soon to be given a class
D800-2 - lower power so should logically have been in it's own class with a lower number than 42
D830 - higher power so should logically have had its own higher class (by analogy with class 29 which used the same diesel)
Class 21 - why weren't the lower powered pilot batch given a lower number? Would they have originally been class 20 with the EE type 1 becoming 18 or 19?
Class 25 - despite the different electrics they all came from the same supplier and had the same power rating so no need for differing class numbers?
Class 17 - the two with Rolls Royce engines had the same power output as the rest so didn't need a different class number - but then you have to explain the 45/46 split

Acathater said:

Just some musings.......pure conjecture but to some extent the missing numbers may have worked something like this?

18 - was this originally the one-off "Super Clayton" which I don't think ever ran on BR?
30 - Brush type 2 with original engines. But what about the uprated ones?
32 - Has been claimed to be on the original draft of TOPS for the Hastings class 33
34 - Known to have been originally intended the pushpull class 33
36 - 10000 / 10001 precursor to the 37, slightly less power than 37 so closest lower number
38 - 10201 / 10202 precursor to the 40, but lower power (type 3)
39 - 10203 revised uprated type 4 precursor to the 40. Different class as different power output
41 - D6XX ?
49 - DP2 prototype for the 50s so given one number less?
51 - Lion? Its Sulzer engine was never downrated which may have resulted in a higher class number than the 47?
54 - Wasn't this intended for the "SuperDeltic"?

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Interesting, but
The "Super Clayton" was 1500hp so would have fallen between classes 31 and 33.
The Ivatt twins were 1600 hp so should have fallen between classes 33 and 35.
Both types, and the Southern trio, were withdrawn in 1963/64, surely long before the classification system was devised. (in 1963 there were many more thanseven "small2 shunter types)

The Super Deltic would have been 4000 hp or more, so would have had a class number higher than 55

Acathater said:

18 - was this originally the one-off "Super Clayton" which I don't think ever ran on BR?

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I bet that’s a loco that has no surviving audio!

I have written about this before but I used to work for a person who was involved in the class designation work, when he was a senior clerk for the CM&EE BRB in the mid 1960’s.

His name was Cyril Beal and he succeeded Arthur Smith (ex Top Shed) as head of the Technical Clerical section (the “KM”) at DME KX in 1969 and held that job for 14 years, when the office shut. He retired to live in Sandy but passed away a few decades ago now.

I worked for him between 1978-80 and occasionally afterwards, filling in for others. He was a kindly soul, very good on stores work, but old school, so “trainspotter” questions would be out of the question.

He said the scheme came about as the CM&EE was getting fed up with everyone calling locos by different names/numbers or in the case of Brush Type 4, the same thing for both what became a 46 or a 47. The latter were sometimes called Hawker-Siddeleys on ER in their early days to differentiate them.

Anticipating that, sometime in the near future, coding for computer systems would be important, there was a need for a class system. It was devised to be a progressive number system based on horsepower and ideas started to be formulated around 1966/67 so everything that existed then would have been included in the drafting. He didn’t do the scheme himself.

The idea was that one offs would not get their own class number if they were part of a larger generic class and for some class numbers (especially the shunters) different builders would be grouped into one class, the 24xx and 25xx both being 05 being a good example of this.

He did volunteer that the scheme went awry when it came to the type 2 locos. The CM&EE wanted the major classes grouped together so that is why we got 24/25 and 26/27 as they are, rather than allocated in strict HP order.

Gaps were left for future builds and, looking at the scheme from the perspective from someone who has been a M&EE Tech Clerk, I strongly suspect that the D600 locos were indeed going to be class 41 but when the scheme was finally published, they and others had gone, as seemingly has any relevant paperwork from that era, so we can only now guess.

The twenty Generators are always the ones that stand out to me. Enough differences that they had restrictions on what air-conditioned stock they could/couldn't haul yet just lumped in with the rest of the 47s, even though Class 48 was assigned to five Sulzer V12 engined examples (although they were converted to Standard 47s before TOPS renumbering). But they didn't even get their own subclass, eg remain 47401-47420 but then start the ETH conversions from standard locos as 47/5 at 47501.

norbitonflyer said:

However, it was the adoption of TOPS that necessitated the actual renumbering, as the system couldn't be adapted to cope with D and E prefixes

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We have discussed this one before. TOPS was bought off the shelf from the Southern Pacific railway in the USA, who didn't renumber their locos when they devised it, had numbers from single up to four digits, both prefix and suffix letters, had classes' numbers split up randomly, had the associated Cotton Belt railway which (due to a longstanding legal issue) as policy had about 10% of each SP loco batch assigned to them with a completely different number scheme, but which locos were actually used as a general pool systemwide, and finally had to cope with locos (and rolling stock) from all across the USA extensively running through onto their system, and into TOPS records.

As it could cope with all that, the BR loco numbering system as stood would be straightforward. If someone wanted it consistent, OK, but not needed for TOPS.

I suspect it was more that staff had developed informal approaches, such as allocating "3150" to a London to Manchester train, and just knowing it was a main electric loco and not a diesel shunter. In the USA loco numbers are very formal, and used in train orders for identification of a train, including the owning railroad's initials if not the home operator, hence why they appear multiple times on the front and are illuminated at night, and everyone is used to precision.

The class 52s were on TOPS with their 10nn numbers until withdrawal.

Remember also that there would be duplication of numbers with coaching stock. 34xxx being Mk1 BCKs for example. 41xxx being Mk3 FOs etc.

On a side note, Translink in NI had to add 8000 to all unit/loco numbers at one point because there were cases of trains being allocated to bus services!

Wasn’t there a plan for a Class 38 type 3 loco to replace the 37s. I think it was killed off by choosing to build class 60s. I see to remember reading about this in Rail in the late 80s.

Merle Haggard said:

The class 52s were on TOPS with their 10nn numbers until withdrawal.

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That was probably because the 52s (and 35s) had metal, rather than painted bodyside numbers, and the cost of replacing them was probably not considered worthwhile.......

dubscottie said:

Remember also that there would be duplication of numbers with coaching stock. 34xxx being Mk1 BCKs for example. 41xxx being Mk3 FOs etc.

On a side note, Translink in NI had to add 8000 to all unit/loco numbers at one point because there were cases of trains being allocated to bus services!

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Not relevant with the loco class scheme as this predated TOPS by several years.

Coaching stock could always be prefixed on TOPS and was with NPCCS, on TOPS way before passenger carrying stock was added. BR wagons were also prefixed.

Class 41 was reallocated to the prototype HST power cars, before they were reclassified as coaching stock.

When TOPS was introduced it was only for freight stock but the records were only of the wagon number not the prefix. From chance enquiries I discovered that duplicate numbers were on the records.
For instance at that time both an ex LMS 'medfit' (3-plank) wagon numbered 450000 (probably actually prefixed 'DM' rather than 'M') and pioneer 45T GLW air braked wagon 450000 were in traffic and on the system. I was trying to locate the 'Supervan' and entering a wagon enquiry for '450000' could produce records for either wagon apparently randomly. Possibly a case of which had moved most recently.

When an area was 'cutover' to TOPS a happy Sunday overtime could be obtained by walking around the area recording every wagon number. This included grounded van bodies and other wagon traces to check if these were still on the Central Wagon Authority's Registry - which they sometimes were. I recall that, as the TOPS implemented area grew larger, - at one stage, from memory, just leaving the West of England - the number of wagons recorded at the CWA but not on TOPS was considerably larger than suggested by the capacity of the remaining area. I don't know - but would be interested to learn - how many wagons were written off CWA records because they evidently no longer existed. However, CWA records were always a bit sketchy; someone I knew slightly visited Turkey to track down the Stanier 8Fs and at the back of some remote shed he found a Southern Railway 25T brake van, still in faded livery. (These had been used as additional brake power coupled in front of the loco on supply trains). On his return from holiday he phoned the CWA with its number - and it was still on the records

Bevan Price said:

That was probably because the 52s (and 35s) had metal, rather than painted bodyside numbers, and the cost of replacing them was probably not considered worthwhile.......

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Indeed, but it shows that a 5 digit loco number wasn't a logical requirement for TOPS. As an aside, when the 52s were withdrawn the loco record would show as (for example) '1023 TOBESCRAPPED', suggesting the loco record didn't even have to be numeric, and could be long.

Gloster said:

I believe that it was introduced internally in 1968, although when in 1968 I know not.

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The new classification was introduced in summer 1968, roughly coincident with the end of steam.

The new classification quickly became public because it was used in the monthly locomotive stock alterations published by magazines. For example, Railway Observer published the new classification in its September 1968 issue, and used the new classification from that issue.

Taunton said:

TOPS was bought off the shelf from the Southern Pacific railway in the USA, who didn't renumber their locos when they devised it, had numbers from single up to four digits

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Merle Haggard said:

When TOPS was introduced it was only for freight stock

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BR considered locomotive fleet renumbering in 1971, in the context of TOPS, but rejected it on cost grounds. The 1971 decision was that new locos would adopt class numbers, starting with class 87, but there would be no systematic renumbering of all of the locomotive fleet. There seems to have been a bit of mission creep: Doncaster Works renumbered classes 83 and 84 as they came out of store prior to the north WCML electrification, as if they were new, and "renumber electric locos" somehow got extended to class 76 too.

The decision to renumber (almost) the whole locomotive fleet came in early 1973 and the main thing that had changed since 1971 was the rapidly growing numbers of locomotives retro-fitted with ETH. These conversions not being confined to recognisable batches of fleet numbers made it more and more difficult, for both the engineers and the operators, to recognise which locomotives had ETH.

Fleetwood Boy said:

When did it become the practice to utilise subclasses (eg 47/0) i wonder?

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Subclasses first "went public" when the renumbering list was published in summer 1973, the subclasses are in Railway Observer for August 1973. However, a problem quickly arose because the engineers and the operators were using different subclassifications, and it isn't clear how long these had been in use internally. There was a revision of the subclassification in 1974 to a single version used by both the engineers and the operators.

Harpo said:

47s were all DB very early on and had been done by the time I was training in 1978.

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You didn't miss vacuum only class 47s by very much, the last to be dual braked were in 1976.

Here is a picture of vacuum only 47102:

Ashley Hill said:

Wasn’t there a plan for a Class 38 type 3 loco to replace the 37s.

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The class 38 project dates back to the 1970s. It was killed off by the 1979 general election result.

Magdalia said:

Subclasses first "went public" when the renumbering list was published in summer 1973, the subclasses are in Railway Observer for August 1973. However, a problem quickly arose because the engineers and the operators were using different subclassifications, and it isn't clear how long these had been in use internally. There was a revision of the subclassification in 1974 to a single version used by both the engineers and the operators.

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Some of the subclasses, or a version of the subclasses, were public before 1973. My 1970 Ian Allan book has the subclasses 33/1, 33/2, 33/3 for what later became 33/0, 33/1 and 33/2. Similarly 31/1 and 31/2 for what became 31/0 and 31/1. Others listed were 17/1, 17/2 and 17/3 for the three variations of 17, 26/1, 26/2, 27 for BRCW Type 2, 24/1, 24/2 and 25 for BR Type 2. Interestingly there were no subclasses listed for 25 or 47, just 47 or 48 for the latter but that may be because the process was still evolving as you say.

The introduction to the book says that the classification system was introduced at the same time as the decision to drop the "D" prefix in 1968.

Interesting the comment about the Type 2 24/25 & 26/27 being paired together, because that did not apply to 21/29. Perhaps the writing was already on the wall for 21 by the time the classification was being drafted.

Magdalia said:

The decision to renumber (almost) the whole locomotive fleet came in early 1973 and the main thing that had changed since 1971 was the rapidly growing numbers of locomotives retro-fitted with ETH. These conversions not being confined to recognisable batches of fleet numbers made it more and more difficult, for both the engineers and the operators, to recognise which locomotives had ETH.

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Curiously that was just the sort of issue that TOPS addressed, that locos could be readily identified on TOPS terminals by their principal fitments. On SP it showed usefully which locos had cab signals (a USA standard) fitted, and/or which were reported as not working, which was used to devise which loco could lead in a typically-USA multiple unit formation in cab signal territory, and which had to stay inside. It later got used for which locos had Locotrol Distributed Power controls. For operators recognition, they just painted large decals about all this on the loco side.

Siemens Staines said:

Some of the subclasses, or a version of the subclasses, were public before 1973. My 1970 Ian Allan book has the subclasses 33/1, 33/2, 33/3 for what later became 33/0, 33/1 and 33/2. Similarly 31/1 and 31/2 for what became 31/0 and 31/1. Others listed were 17/1, 17/2 and 17/3 for the three variations of 17, 26/1, 26/2, 27 for BRCW Type 2, 24/1, 24/2 and 25 for BR Type 2. Interestingly there were no subclasses listed for 25 or 47, just 47 or 48 for the latter but that may be because the process was still evolving as you say.

The introduction to the book says that the classification system was introduced at the same time as the decision to drop the "D" prefix in 1968.

Interesting the comment about the Type 2 24/25 & 26/27 being paired together, because that did not apply to 21/29. Perhaps the writing was already on the wall for 21 by the time the classification was being drafted.

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An interesting oversight made by whoever drew up the list of new numbers.
The -/1 subclass was given the lowest numbers in the class, so started at 001. If those numbers didn't reach 99 then the /2 sub-class would start at 101.
This created the situation that, in classes with sub-classes, there was a confusing mis-match between the number group carried by a loco and the sub-class - usually, the numbers were 100 higher than might be expected
This anomaly was removed by making, for instance, the former /1 subclass the /0 one so that the painted numbers than matched. Involved a lot of repetitive paperwork I imagine but I wonder why whoever drew up the renumbering list didn't think of that problem. DB/DR had used the system of loco number indicating both class and sub class for many years..

Merle Haggard said:

This created the situation that, in classes with sub-classes, there was a confusing mis-match between the number group carried by a loco and the sub-class - usually, the numbers were 100 higher than might be expected
This anomaly was removed by making, for instance, the former /1 subclass the /0 one so that the painted numbers than matched.

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This was one of the features of the 1974 revision.

Taunton said:

We have discussed this one before. TOPS was bought off the shelf from the Southern Pacific railway in the USA, who didn't renumber their locos when they devised it, had numbers from single up to four digits, both prefix and suffix letters, had classes' numbers split up randomly, had the associated Cotton Belt railway which (due to a longstanding legal issue) as policy had about 10% of each SP loco batch assigned to them with a completely different number scheme, but which locos were actually used as a general pool systemwide, and finally had to cope with locos (and rolling stock) from all across the USA extensively running through onto their system, and into TOPS records.

As it could cope with all that, the BR loco numbering system as stood would be straightforward. If someone wanted it consistent, OK, but not needed for TOPS.

I suspect it was more that staff had developed informal approaches, such as allocating "3150" to a London to Manchester train, and just knowing it was a main electric loco and not a diesel shunter. In the USA loco numbers are very formal, and used in train orders for identification of a train, including the owning railroad's initials if not the home operator, hence why they appear multiple times on the front and are illuminated at night, and everyone is used to precision.

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I have seen it stated before that the "TOPS renumbering" wasn't actually for TOPS, but for the introduction of RAVERS.

Magdalia said:

The class 38 project dates back to the 1970s. It was killed off by the 1979 general election result.

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If that had killed off the Class 38 project it reappeared in the 1980s. The six Class 37/9 conversions were for testing proposed power units for the Class 38. What finally killed Class 38 off was Railfreight changing their requirement to a Type 5 heavy haul loco - what we now know as Class 60.

Merle Haggard said:

An interesting oversight made by whoever drew up the list of new numbers.
The -/1 subclass was given the lowest numbers in the class, so started at 001. If those numbers didn't reach 99 then the /2 sub-class would start at 101.
This created the situation that, in classes with sub-classes, there was a confusing mis-match between the number group carried by a loco and the sub-class - usually, the numbers were 100 higher than might be expected
This anomaly was removed by making, for instance, the former /1 subclass the /0 one so that the painted numbers than matched. Involved a lot of repetitive paperwork I imagine but I wonder why whoever drew up the renumbering list didn't think of that problem. DB/DR had used the system of loco number indicating both class and sub class for many years..

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The Class 25 subclasses did not follow the rules, however.