Aldenham & 'CU' numbers

Identity swapping between vehicles of identical make and model went on from the time that the LGOC moved its overhaul systems to the new Chiswick works in 1922. This meant that as a vehicle went into works for overhaul its identity was taken over by a freshly overhauled vehicle. The system operated through the London Transport era until the mid eighties when rules were changed in the run up to privatisation of the bus industry. During the war, the normal system of overhauls was suspended and afterwards, the Ministry of Transport & Civil Aviation (as it as then known) decided that they would tighten up on vehicle testing regimes and in order for LT to carry on with the pre war system they had to be able to identify each chassis so as to trace its history. The system was created by a Mr Charles at Chiswick and was initially known as the 'Charlesian' system. It came into operation part way through the first cycle overhauls of RTs in 1951 but pre war vehicles were not affected as there were no plans to extend the 'works float' system to them due to their being life expired and due for withdrawal. This meant that the majority of STLs and earlier classes did not receive 'chassis unit' numbers (cu for short). It was later extended to cover the last two batches of the T class, T769 - 798 (14T12 & 15T13), the 131 TDs, STD 112 - 176 (the 4STD3s) and the GSs, RLHs and RFWs and this despite the fact that each of these classes was not involved in works float identity swapping. Specifically excluded because of their date of origin being 1940/41 were the 2RT2s and the Utilities which dated from 1942 - 46.
The first chassis to receive a cu number was that of RT 426 which received the number 1001 when it went in for overhaul on 11th April 1951 (the chassis was sent to Chiswick for overhaul on the 18th, a common practice with RT family vehicles until well into 1954). As vehicles arrived for overhaul, the chassis' were allocated their cu numbers and these are, therefore not in sequence with any of the other identifcation numbers i.e bonnet no, chassis no, body no etc. They are, however, for the most part in sequence with the date of first but, in the case of some RTs, their second overhaul. This resulted in some RTs with low chassis or bonnet numbers being given cu numbers in the 3xxx range as they did not receive their next overhaul until 1954. When the full blown works float system started in early 1955, Aldenham began working on the principle of 'a bus in today goes today', perhaps an over simplification of the system as it didn't always happen but it meant that the licences were in use for the maximum amount of time. The RTWs, RTLs and RFs had their cu numbers applied in almost the exact sequence of their date of first overhaul, the only exceptions being where a vehicle went into works late for some reason. There are, however, two exceptions to the above general rule and the first was the SRT class, which was, for some reason, allocated a series of cu numbers which commenced at 101 for SRT 1 and ran in sequence with the bonnet numbers with SRT 160 being allocated the cu number 260. Most SRTs were not overhauled but evidence suggests that these cu numbers were not actually applied to any of the SRT chassis. The other exception to the rule concerns the 160 RT chassis (RT 4397 - 4556) which were purchased to take the bodies from the SRTs when they were withdrawn. These were allocated the cu numbers 2401 - 2560 and they were the only RT family chassis' to carry cu numbers from new as they were affixed when the vehicles were delivered to Aldenham or Chiswick for fitting of the bodies. The cu numbers ran in four separate sequences within this batch but within each sequence they are in the correct order with the bonnet numbers. Paradoxically, this is the only batch of RTs where the body numbers are not in sequence with the bonnet numbers as delivered new. Very fortunately for us, meticulous records were kept of both chassis and body changes on the rolling stock record cards so that we can not only trace the full history of every RT body but also each chassis as well. These were not the only records that LT kept as each major component of a vehicle carried its own identifying number on a plate which also gave the date of last overhaul of that component. This covered engines, gearboxes, dynamos, compressors, radiators, front & rear axles, cardan (prop) shafts, springs and even wheels. When a vehicle was sent out after overhaul it carried a card with details of all the major units and any changes would be noted by the garage staff on this card. Unfortunately, very few of these cards survive or we would be able to trace this history of every major component of every London RT family bus. The one item that has survived are the original LT engine numbers which are shown on the rolling stock record cards and also on the daily variation sheets and from these we can ascertain the origin of many of the surviving engines, always supposing that their identity plates still survive.

I have attached a facsimilie of the front of the rolling stock record card for NS 144 which shows that for the most part NS 144 went in and out of works for overhaul in a maximum of four days throughout its life with the LGOC. The same principle applied to the vast majority of London bus overhauls from 1922 until the mid 1980s.

Alan Bond
04/2012

13/04/12 - 17:44

Alan - Amazing!
Thank you for your explanation of cu numbers; although I was aware of body swops within Aldenham, I had no idea that chassis were also swopped.

Bob Gell

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