U-Series Model Evolution
What follows, at Phil Wormald's request, is an updated and edited version of my various recent postings - and the responses thereto - on the World-Diesel-Loco mailing list (WDL). As such it is certainly not the outcome of scholarly research nor meticulous study, so is hardly definitive. Rather, I have simply used those sources and resources, both internet and print, that were readily available to me, combined with information kindly provided by correspondents. Because there are significant gaps in my knowledge, there are corresponding gaps in this essay. Some I have tried to fill by deduction and speculation, the risk of error notwithstanding.
Perhaps this kind of "amateur" effort can be justified simply by the fact that there has been very little written on the subject of GE exports to date. Certainly, the much-appreciated positive feedback I have received about my WDL postings suggests that there is a place for it among Railfans "hungry" for information on GE models. In that spirit, it is presented as a "work in progress", readily updated, that will serve as a platform for further fruitful discussion on WDL.
GE U-Series - Initial Model Range
GE launched its 9-model U-series range in early 1956. The earliest trade advertising I have seen dates from April, 1956. GE was later than both General Motors (GM) and Alco in offering "mass-produced", standard models for the export market, but from the start it listed a much more comprehensive range. It may well have influenced GM and Alco, both of whom in the next few years were both advertising much wider standard model ranges. However, it is important to note that since the late 1940s, GE had been quite active in the export diesel locomotive market with what might be described as a quasi-standard model line, as well as, through 1953, being involved in Alco exports through the Alco-GE partnership.
The initial nine U-series models were the U4B, U6B, U9B, U9C, U12B, U12C, U18B, U18C and UD18B.Of these, seven, namely the U4B, U6B, U9B, U9C, U12B, U12C and U18C were clearly designed, both dimensionally and weight-wise, with narrow-gauge (Cape, metre and 3 foot) applications in mind, although they were readily adaptable to broader gauges, ballasted if needs be. The same narrow-gauge "bias" was evident in GE's pre-U-series export models.
The other two models, the U18B and UD18B, were intended for standard and broad gauge applications. All were hood units; of the end-cab type in the case of the U4B and U6B, and of the road-switcher type for all of the others. In contrast, some of GE's pre-U-series models were cab units. It is convenient to divide the nine original models into three groups for further study of both them and their successors, namely:
The Small End-Cab Models
The initial U-series, as announced in 1956, included two small end-cab variants, namely the U4B and U6B. They shared a common, 33'6" frame. The U4B, 400/340 (?) hp, had the 8-cylinder Caterpillar D375 engine, whereas the U6B, 600/540 (?) hp, had the 12-cylinder Cat D397 engine. The U6B can be seen as the U-series follow-on to the previous Cat D397-engined 52 ton model, production of which continued into the U-series era.
The U4B was never built, and the first U6B models, for United Fruit Costa Rica, were not built until 1959. By that time, the Cat D397 engine had been up rated to 700/640 (?) hp, in place of the 600/540 hp originally listed for this model. Early in 1960, GE advertising in respect of the export U-series mentioned just four basic power categories, namely U6, U9, U12 and U18. So it seems that the idea of a Cat 8-cylinder-engined small model was temporarily in abeyance. Only 28 Cat D397-engined U6Bs were built before the first set of model changes arrived.
Meanwhile, the particular Cat engine series had been further updated, with the D379 (8-cylinder) and D398 (12-cylinder) replacing the D375 and D397 respectively. This resulted in the release of two new GE models, the U5B, 600/540 hp, (Cat D379) and U8B, 900/810 hp, (Cat D398), first built for RFFSA, Brasil in 1961. These two appear to have been direct replacements for the original U4B and U6B respectively.
By mid-1962, the UM10B had been added to the model range, supplementing the U5B and U8B. It was essentially the U8B with the Caterpillar D398 engine up rated to 1050/950 hp. The use of a "UM" designation for what was a standard model appears to be perverse, and it seems that by the time the first of these locomotives were built in 1964, the designation had reverted to U10B. It is possible that GE had initially "reserved" the U10B designation for a notional follow-on to the U9B, and so was compelled to find an alternative for the up rated U8B.
The UM10B designation was later "recycled" for at least two modified U10B derivatives, which will be discussed later on.
The GE entries in Jane's 1969-70 and 1973-74 both list the U6B, Cat D379 engine, 700/640 hp and the U10B, Cat D398 engine, 1050/950 hp. So somewhere between 1962 and 1969, the U5B became the U6B. Basis Phil's export listing, the first D379-engined U6Bs were built in 1965.
This was a recycling of the U6B model designation, which might be a bit confusing in and of itself, and made more so by the specific Cat engine designations. That is, the early U6B had a Cat D397 12-cylinder engine, whereas the later edition had a Cat D379 8-cylinder engine.
Jane's 1981-82 lists the U10B, 1050/950 hp, and U11B, 1100/1000 hp, respectively with the Cat D379 and Cat D398 engines. So between 1974 and 1981, there has been a further up rating of the engines, with the U10B and U11B replacing the U6B and U10B respectively. Again basis Phil's list, the U11B seems to date from about 1974. Even so, the U6B was built until 1992, long after the D379-engined U10B was released. And it's possible that the D379- and D398-engined U10B variants were built in parallel. Anyway, this recycling of the U10B model designation simply adds to the potential confusion.
There was also a U11B variant, built for Rhodesian Railways, fitted with the Pielstick 8-cylinder PA4200 engine.
The following table provides a summary of the standard, Cat-engined end-cab models from 1956 through to the early 1980s.
The Intermediate Road Switchers
The initial 1956 U-series included four intermediate road switcher variants, namely U9B, U9C, U12B and U12C. All shared the same, 46'4½" long frame. The U9B and U9C had the 6-cylinder CB FWB-6L engine, at 990/900 hp, whilst the U12B and U12C had the 8-cylinder CB FVBL-8 engine, at 1320/1200 hp. The U9B and U12B were Bo-Bo (B-B), and the U9C and U12C were Co-Co (C-C).
All four variants were built from 1957 onwards. However, the U9B and U9C sold in small numbers only, and the last, a U9B for RFFSA Brasil, appears to have been built in early 1959. The U9 was still offered by GE in early 1960, but was evidently discontinued by mid-1962. In this power range, it seems that the major market was for simpler, 'utility' locomotives like the U8B and GM GL8, rather than for full road locomotives like the U9 and GM G8. And where full road locomotives were required, Alco had a better-matched product with its DL531/DL532, which was, in baseline form anyway, shorter and lighter, and one assumes, less costly than the U9C/U9B.
Whether GE ever "re-rated" the U9B/U9C and listed it as the U10B/U10C I do not know. Had the 6-cylinder model remained in the product line at the time the U12B/U12C became the U13B/U13C, it would have been logical for it to have undergone a like transition. That would also explain GE's temporary use of the UM10B designation for the up rated U8B. There might have been a short overlap period in which both the U10B and UM10B were listed.
The U13, with the CB FVBL-8 engine re-rated to 1420/1300 hp, was released sometime in 1960. It is not mentioned in early 1960 GE advertising, which still refers to the U12. However, the U13C was, for example, included in a Goninan-GE tender submission to NSWGR, Australia, late in 1960, along with the (12-cylinder) U18C. This mild re-rating of the CB 8-cylinder engined model, with no corresponding change in the 12-cylinder model (U18C) is curious. One can wonder whether GE wanted to be able to match the power stated output of the GM G12/GR12 (1425/1310 hp) albeit with a somewhat lighter locomotive, or perhaps keep a distance from Alco, whose noticeably lighter 1350/1200 hp DL535 was released late in 1961. (One assumes, that GE, as electrical equipment supplier, was well aware of Alco's intentions.) It may have been that GE arranged for the change in designations to correspond with other progressive improvements that were specific to the U12 and U18C models, and were not made at the same time.
The re-rating was simply a restatement of the engine power output as measured under UIC conditions. There was no actual change in engine rack settings. Previously, GE had quoted outputs that were available at up to 5000 ft elevation and 113°F ambient temperature. Under the milder UIC conditions, the numbers were naturally a bit higher. Thus, the 8-cylinder engine went from 1320/1200 to 1420/1300 hp. The numbers for the 6-cylinder engine would, one supposes, have gone from 990/900 to 1075/985 hp, although I have not seen any confirmation of the latter numbers.
Within the next few years, and I think by 1964, the U13 had a body-style change, from high-short-hood to low-short-hood, using the longer version of the GE 'nose'. Also, the engine designation was changed from CB FVBL-8 to GE 7FDL-8. Whether these two events were concurrent I don't know. I say that they likely happened by 1964, because that was the year that the U20C version of the 12-cylinder model was first built, with low-short hood and GE 7FDL-12 engine. However, in mid-1962, the U13 still had a high short hood, and U13Bs in this form were supplied to RFFSA, Brasil in the first half of 1963.
That low-short-hood U13Cs were built is certain, but I don't whether there were any such U13Bs. Basis Phil's production list, the last U13Bs seem to have been built in 1963. I had previously assumed that, perhaps through lack of demand, GE dropped the Bo-Bo option about then or shortly thereafter. However, I am advised that the U17B was still listed in Jane's 1973-74.
The next iteration was the U15C, mentioned in Jane's 1969-70, albeit accompanied by a photo of Chilean low-short-hood U13C Dt-13101! The U15C had the GE 7FDL-8 engine up rated to 1650/1500 hp. Here again the 8-cylinder model led the way, as there was no up rating of the 12-cylinder engine between 1964 and 1971. The Jane's 1969-70 listing is not comprehensive in respect of GE export models, and there is no mention of a companion U15B version. However, basis the listing of the U17B in 1973, it's reasonable to assume that GE also listed a U15B, even if it never built one.
I'm not completely sure about this, but although the initial U15C as envisaged by GE might have had the long-low-short-hood form, this model was actually built from the start with the short-low-short-hood body form, and with the high adhesion bogies (trucks) in place of the outside-equalized type used on the U12C and U13C.
So, perhaps unintentionally, the U13C-to-U15C transition also marked a change in body style and bogie design.
Jane's 1981-82 lists two 8-cylinder models, namely the U15C and U18C. The 1650/1500 hp U15C is as before. The 1950/1820 hp U18C shares the same frame and base weight, but has an up rated 7FDL-8 engine coupled to a GTA11 alternator. Basis Phil's list, the first 8-cylinder U18Cs were supplied in 1976, although the model might have been announced earlier. There was a domestic model, the U18B, built from 1973 with the 7FDL-8 engine at the 1800 hp (tractive) rating. So the 225 hp/cylinder (tractive) version of the 7FDL-8 was available at least from 1973.
One can infer that the U17B and U17C were first offered in the early 1970s in addition to, rather than in place of the U15B and U15C respectively. Then, the U17C was superseded by the U18C by 1981, whilst the U17B had no successor. Whether the U17 was DC/DC, like the U15, or AC/DC, like the U18C, I do not know.
Note that U18C model number was recycled for the 1950/1820 hp 8-cylinder variant. It was originally applied to the initial 12-cylinder model in 1956, and built through 1961.
I think that the U18C is still current, but so far I haven't looked very closely at the model progression since the early 1980s. I am aware that there has been a further increase in power output of the 7FDL-8 engined model, in the form of the U20C, available from 1995, maybe earlier. As GE is wont to do, the U20C model number was recycled from the long-lived (1964-1980+) 12-cylinder U20C, perhaps the most widespread and best known of its export models. There may even have been some overlap, as the first 8-cylinder U20Cs appear to have been built for Indonesia in early 1995, whereas GE Brasil built 12-cylinder U20Cs at least until late 1994.
In 1975, Sudan Railways received an unusual A1A-A1A bogied U15 variant. This was likely a customer request, as GE had been on record as being against this wheel arrangement. Maybe Sudan railways wanted these GE's for the same light-rail applications for which it had previously acquired some A1A-A1A-bogied Hitachi-MAN locomotives with 12½ (long) ton axle loading.
Similarly, Indonesian Railways had some U18A1A models delivered from 1977, although these were later rebuilt as U18Cs. The U18A1As may have continued a 'tradition' started with the GM G8s in 1957; it's possible that for light rail applications, there are situations where, at a given axle loading, locos with A1A bogies are kinder to the track than those with Co bogies.
There is a possible U12C derivative in the form of the four 600 V DC electric locomotives supplied to Anglo-Chilean Nitrate 1958/60. This is a purely deductive comment, though: they look like electric U12Cs, their weight, 90 (short) tons is about the same, and Anglo-Chilean Nitrate also had some U12Cs.
The following table provides a summary of the intermediate road-switcher models from 1956 through to the early 1980s.
The Larger Road Switchers
The initial GE export U-series, as announced in 1956, included three road switcher models fitted with the CB 12-cylinder FVBL-12 engine set at 1980/1800 hp. These were the U18C, U18B and UD18B.
The U18C, with the same Co-Co (C-C) bogies (or bogie options) as the U12C and U9C, but with a longer (52'0") frame, was, like all of the smaller models previously discussed, designed primarily to meet narrow (3 foot, metre and Cape) gauge requirements, but was readily adaptable to standard and broad gauges.
The U18B and UD18B were both intended for standard and broad gauge applications only. The U18B was essentially the U18C mounted on the same domestic-style Bo (B) bogies as used under the UD18B. As far as I know, none were built. Its 23½ (long) ton axle loading would surely have limited its utility on most non-AAR-dimensioned standard gauge roads in the late 1950s. The U18B designation was eventually recycled for a much different (8-cylinder) domestic model in 1973.
The UD18B was clearly of US domestic proportions - 14'7" high and 10'0" wide, and effectively was a forerunner to the domestic U25B and all that followed. It was built in 1956 only for the NdeM. And unlike its eight siblings in the original GM U-series stable, it has been well mentioned in the American literature. I've never ascertained the significance of the 'D' in its model designation. Fairly obvious candidates are 'Demonstrator' and 'Domestic', but I've also wondered whether it might have come from 'heavy Duty'.
Anyway, neither the U18B nor the UD18B had successors in the GE export U-series, so have little to do with the model progression since 1956.
That takes us back to the U18C, which was built from 1957 in heavier, standard and broad gauge as well as lighter, narrow gauge forms. For narrow gauge applications it offered, by the standards of the time, quite high power in relation to its baseline weight and axle loading of approximately 90 and 15 (long) tons respectively, with a relatively compact profile, 12'0" height x 9'0" width. Nor did the high power come with any low speed performance liabilities; with standard gearing for 60 mile/h top speed, it had a minimum continuous speed of 10 mile/h, at which its tractive effort was 51 000 lbf, corresponding to 25% adhesion. Looking at its American competition, the 1950/1800 hp Alco DL500 was already established, and although nominally available in narrow gauge form, it was evident that it was configured more with standard and broad gauge applications in mind, having a profile that fitted the Bern loading gauge and with axle loadings that started at 16 tons and were usually higher. The same would apply to the DL541, still in the future. GM's heavier, longer, higher and wider 1950/1800 hp G16 was also still in the future, as was its GR12, which, for the saving of a just couple of tons or so, provided only 1425/1310 hp, making it more of a drag service locomotive. So, in the narrow gauge world, the U18C was really quite a landmark locomotive.
Next in sequence was a special variant, the U18C1, with 1-Co-Co-1 (1-C-C-1) wheel arrangement and consequent low axle loading, built 1959-61 only for South African Railways. This seems to have been viewed as a non-standard model by GE, and was not, for example, included in its mid-1962 model listing. Although there is evidence that GE was not keen on departing from the all-adhesion concept, the U18C1 was nevertheless the outcome of some careful design effort. Its bogies were designed for high adhesion, bearing in mind that by the standards of the time, the power-to-adhesive weight ratio was quite high, at 24 hp (tractive) per (long) ton. Not until the U26C of 1971, at 27 hp/ton, did GE exceed this ratio in a standard model.
The last of the South African U18C1s, supplied late in 1961, also appears to be the last of the original U18 models built. There follows a hiatus from the second half of 1961 until 1964, when the 2150/2000 hp U20C was first built, and in low short hood form.
As previously noted, the announcement of the U20C appears to have lagged that of the U13, but it was listed, in high short hood form, by mid-1962, and with a baseline weight that, at 86.8 (long) tons, had been pared down a bit as compared with the U18C.
The 2150/200 hp numbers were simply a rerating of the 12-cylinder engine to conform to UIC practice. It's interesting to note that late in 1961, Alco had announced its 2150/200 hp DL-543, described as being for restricted clearances and 16 tonne axle loadings. However, like the DL-500 and DL-541 before it, the DL-543 was still a Bern loading gauge machine, and I think only 3 or 4 were sold for narrow gauge applications. To put Alco's description into perspective, the contemporary DL-535, just a tad more compact in profile than the GE U-series models, was described as being for 'extremely reduced clearances'. Notwithstanding these differences, the U18C had sold well to standard and broad gauge railways.
The U20C retained the same 52'0" frame as the U18C, but by the time the first were built in 1964, the longer version of the GE low short hood had become standard. And the engines wore the GE 7FDL-12 nameplate. So in this case, as it turned out, the change of model designation, change of power output numbers, change of engine/engine designation, and change of body style were all coincident.
There was a small build of the U20C1, a 1-Co-Co-1 bogied variant, for South African Railways in 1966, which like the U18C1, appears to have been viewed by GE as non-standard.
The body style was changed to the short-nosed low hood form, and high-adhesion bogies adopted circa 1970/71. I'm not sure exactly when this was, but I'm fairly certain that some railways, such as those in Zambia and Mozambique, had both U20C body-style variants. Unlike the case with the 8-cylinder model, in which the body-and-bogie transition in fact corresponded to the U13C-to-U15C transition, there was no change in power output or model designation.
There was a major power increase with the introduction of the 2750/2600 hp U26C in 1971. This, equipped with a much-uprated 7FDL-12 engine, was built on a longer (55'6") frame and had the short nose and high-adhesion bogies from the start. It also had an alternator - the first of the export U-series to be so-equipped, and permanent all-parallel connection of its traction motors, which likely aided low-speed adhesion. In baseline form, with variable section frame, it had total weight and axle loading of about 96 and 16 (long) tons respectively, and was built in this form for early user New Zealand Railways. It was also available with heavier, constant section frames, and was so built for the other early user, SAR. GE evidently anticipated that some Cape and metre gauge railways would want much more powerful second-generation diesel locomotives, but that not all of these would be able to accommodate significantly heavier ones.
The U26C was introduced as a new model in the export U-series, and not as a successor to the U20C. So they were both offered and built through the 1970s. GE may have had a bit more competition, in the form of MLW with its MX620 and derivatives. It seems that MLW had reworked the Alco DL-543 into the MX-620, in the process offering both lighter (90 ton) variants that could match the U20C, and more powerful derivatives, all of which were dimensionally suited to narrow gauge requirements. Certainly, during the 1970s/early 1980s MLW picked up some African Cape and metre gauge orders for which GE U-series models were surely good candidates. Also, in the late 1960s, GM had introduced the 2200/2000 hp G26C as the lighter and shorter replacement for the G16C, which could be built to be weight-competitive with the U20C.
The GE entry in Janes 1981-82 listed two 12-cylinder models in the GE export range, namely the 2300/2165 hp, 88 900 kg, DC/DC U22C and the 2750/2600 hp, 96 200 kg, AC/DC U26C, the latter being essentially the same locomotive as released in 1971. On the face of it, the U20C had become the U22C through a mild uprating. A footnote indicated that a streamlined dual-cab version of the U22C was available.
Basis Phil's list, the first U22Cs were supplied to Nigerian railways in 1975. However, it seems that the popular (12-cylinder) U20C, although not included in that Janes list, remained in production at least into the early 1980s. Perhaps the late U20Cs were simply U22Cs reset for lower power output.
The streamlined dual cab version appears to have been the UM22C, first built for Sudan railways in 1976, and later, by Krupp, for Botswana Railways.
Rather uncharacteristically, though, GE has applied the U22C model to a diversity of models. As well as the standard, 'uprated U20C', some 2200 hp (tractive) 'specials' built by Goninan-GE from 1983 for Queensland Railways, Australia, as its 2600 class, were given the U22C model designation. These had the 7FDL-12 engine at the U22C rating, but with AC/DC rather than DC/DC transmission. They had a longer variable-section frame than the U26C, and heroic measures were necessary to keep the weight down to 96 tons. An impressive piece of design engineering they may have been, but the usual description in the literature, which has them as a much pared down version of the standard U22C in order to meet QR's unusually tight weight restrictions, is not quite right. It might be better to consider them as a pared-down version of a notional stretched (from 52' to around 59') U22C, which without special treatment might have come out at well over 100 tons.
And the GE Brasil version of the U22C, built from the mid-1980s, has the 55'6" U26C platform, AC/DC transmission, and a weight range of 96-120 tonnes. It might be viewed as a derated U26C.
I don't think that there has been any advance on the U22C in the 'smaller' 12-cylinder model series, and the U26C has not been directly superseded, either. But perhaps that's because later, non-U-series models have largely taken their place, even in the narrow gauge sphere.
The U30C export model as first built, by Krupp, for the Cape gauge Tazara in 1982/83, is an up rated, heavy frame U26C. The U30C model designation was apparently recycled, having previously been used on a 16-cylinder domestic model, in production until around 1976.
On model number recycling, both the U18C and U20C designations, originally applied to export 12-cylinder models, have been reapplied to export 8-cylinder models. In the case of the U18C, there was a long interval in which it was quiescent, but less so in the case of the U20C. And I think that for many observers, mention of 'U20C' would conjure up images of GE's classic 12-cylinder model, in either long- or short-nose form according to personal preference.
The E42C electric locomotive, as supplied to Taiwan Railways, and body-styling aside, looks as if it might be effectively an AC electric derivative of the U20C or U26C. I think it has 761 traction motors (maybe modified to work with ripple current - possibly even sepex), and U-series type running gear.
The following table provides a summary of the larger road-switcher models from 1956 through to the early 1980s.