Regarding the GE U9 export model, 990/900 hp and powered by the C-B FWB6LT engine, I suppose that in hindsight it was something of an oddity, but that when the Export Universal range was planned, it seemed reasonable to include a fully-fledged road-switcher in the 900 to 1000 hp range. For example EMD had included the G8 model, 950/875 hp road-switcher in its standard export range from circa 1954. In the event, the market for that type of locomotive seemed to peter out after 1960 or so, and GE obtained but a small share of what there was, with 29 total, comprised of 13 U9B and 16 U9C.
The U9 was based upon the same frame as the FVBL8T-powered 1320/1200 hp U12, so shared the same basic dimensions. It had the GT599 main generator instead of the GT581 used on the U12, but retained the triplex auxiliary gear drive system. Generally it was homologous with the U12 and the larger U18 in terms of its control system and features and facilities. On a basic weight basis, it was around 8 000 lb lighter than the U12, so it did not offer major relief in the axle loading department. That it shared a frame with the U12 likely made it heavier and possibly longer than it otherwise might have been, but presumably there was a production cost benefit to GE that gave it more flexibility with both U9 and U12 pricing. By the way, I know very little about the GT599 main generator. It should not surprise me if it shared the same frame size as the GT584, but that is pure speculation.
Anyway, EMD had set a precedent, in that its G8 shared the same frame as the 1425/1310 hp G12. Power-wise, the G8 was two-thirds of a G12, whereas the U9 was three quarters of a U12. And the shared frame probably made the G8 heavyish for its power. I understand that EMD’s original plan included a G6, powered by the 6-567 engine and on the same frame, but perhaps wisely, that idea was not brought to fruition.
In offering both B-B (U9B) and C-C (U9C) variants, GE had stepped ahead of EMD, who offered only 4-motor B-B and A1A-A1A variants of the G8. Whilst GE did not offer A1A-A1A versions of any of the Universals, and at the time was on record as being antithetical to this wheel arrangement, it probably would have built such had any customer asked for it.
GE had announced its export Universal range in the early part of 1956. In the latter part of 1956, Alco announced an extended export model range that included the DL531, of 975/900 hp. This was a light, low-profile road-switcher powered by the 6-251 engine, with GE GT584 main generator and GE761 (or GE764) traction motors. It was available with B-B, C-C and A1A-A1A wheel arrangements, although the last-mentioned was never built. Being designed around the 6-251 engine, the DL531 was noticeably shorter and lighter than the GE U9, with which it directly competed. It was also somewhat simpler. It had a belt-driven exciter/auxiliary generator that was usually associated with the lower end of the power range, although it did have full (Lemp 1914) load control via a Woodward PG governor with integral load control rheostat. It had trimount trucks, probably adequate for its typically realizable operating speeds, whereas the GE U9, like the U12 and U18, had floating bolster trucks. The Alco DL531 might have had a production cost advantage over the GE U9, and I should not be surprised if Alco was aggressive in its pricing. As it did not have a “horse” in the U12 class, it was probably eager for all for the DL531 business it could get. Alco could claim some electrical parts commonality with the GE Universals, so that for example the DL531 would not be out-of-place in a fleet which also included for example U12 and U18 models. But commonality might not have been such a big issue for the target customers, amongst whom the Argentinean and Brasilian state railroads at the time were inclined to spread their business around. A significant early order for the DL531 was that from RFFSA Brasil, who acquired 77, of which 57 were C-C and 20 were B-B. In the same period RFFSA acquired from GE 3 U9B, 52 U12B and 12 U12C.
Anyway, one might say that the DL531 was less compromised than the GE U9 and EMD G8, and it obtained a goodly share of the business on offer through to about 1960, after which the landscape had changed.
GE’s initial Universal range included the small and simple end-cab U4B and U6B models, both B-B only, and with the choice of industrial switcher rigid bolster or floating bolster road trucks. These had Caterpillar engines, GT601 main generators with belt-driven exciter/auxiliary generator and GE761 or GE764 motors. They had simple “inherent characteristic” load control (Lemp 1924), and the engines had Caterpillar governors controlled by an electropneumatic throttle operator. The U4B was never built, and the U6B had a slowish start, but it almost inevitably just a matter of time before the customary power growth moved this design towards 1000 hp, where it would offer a credible alternative to the fully-fledged road-switcher. This part of GE’s Universal range was a logical development of the previous Caterpillar-powered 50, 52 and 54-ton range. The 50-tonner had originated as something of a “smaller brother” to the 70-tonner, and the production of the 50- and 52-ton models continued into the Universal era.
EMD had likely seen the coming trend, and in 1958 released both the GL8 and GA8. Both of these were end-cab models powered by the 8-567 engine, and were shorter and lighter than the G8. The GA8 was the “super-simple” version, B-B with cardan shaft drive and freight-car style trucks. The GL8 was of normal configuration, originally available only in B-B form, although an A1A-A1A variant (in two versions) was soon added. The GL8 did not directly supersede the G8, but once it was in production virtually eliminated sales of the latter except in Australasia. With these models EMD was able to offer some competition for the GE end-cab models, and also extend upwards the power range covered by this kind of locomotive.
Alco in 1961 introduced its 1350/1200 hp DL535, essentially a longer and heavier version of the DL531 C-C variant with an uprated 6-251 engine and GE GT581 main generator, although retaining the belt-driven exciter/auxiliary generator. Alco’s primary objective seems to have been to offer a locomotive that was or could be seen as being proximate to the GE U13 and EMD G12. The DL535 was slightly shorter than the GE U13C, and its base weight was somewhat lower. Alco also may have realized also that the 900-1000 hp bracket was now largely the province of the end-cab unit rather than the road-switcher, and so would have seen the upgrade as pivotal in maintaining its 6-cylinder sales. And in fact, once the DL-535 was available, sales of the DL-531 fell away except in Australia. Whilst the DL-535 may have cannibalized some potential DL-531 sales, it does look as if the market for 900-1000 hp road switchers had largely dried up. As at the time Alco did not have a vee-8 version of its 251 engine, it was obliged to uprate its 6-251. Its resultant seriously high (for the time) mean effective pressure seemed not to be a problem nor did it deter customers.
Against that background, 20/20 hindsight shows that the U9 probably had little chance of selling in quantity. Still, GE kept the model in its range through its power restating exercise circa 1961, whereupon the U9B and U9C became the U10B and U10C respectively, of 1090/1000 hp. But none were built. By then the U6B had been superseded by the U8B, at 900/810 hp, which was fitted with the Caterpillar D398 engine in place of the D397. In the power restating, the U12B/C had become the U13B/C, and the U18C had become the U20C. I suspect that the U10B/C was deleted from the catalogue during 1962. By mid-1962, a more powerful version of the U8B end-cab model had been added as the UM10B. This had an uprated Caterpillar D398 engine, set at 1050/950 hp. Possibly the UM10B designation was used to distinguish this new model from the never-built 6-cylinder U10B. Anyway, after a short interval, the UM10B was renamed as the U10B.
So, the 900 to 1000 hp category was now dominated by the simple end-cab locomotive. That said, the GE UM10B/U10B could be optioned up, with road trucks, MU equipment and dynamic brakes if required. Modest HEP (in the vicinity of 10 to 15 kW), for train lighting, was an option, as on the larger models.
In the mid-1960s though GE did build, as a UM10B variant, a road-switcher version of the U10B for RENFE Spain, and again in the 1970s for OSE Greece. This had an extended frame and a high short hood to accommodate a train heating boiler. This might have been envisaged when the original UM10B was designed. A 1962 September “Diesel Railway Traction” article noted that the train heating boiler was optional on the UM10B and upwards. The U13B/C and U20C had room in the carbody for the boiler, but the basic UM10B did not. Whether the U9B/C and not-built U10B/C had room for a boiler is unknown. Conceivably the 6-cylinder engine, being longer than the vee-8, encroached upon the space set aside for it. By way of comparison, the Alco DL535 required a four-foot frame extension to accommodate a train heating boiler, and this variant was built for RENFE Spain as the DL535S and for OSE Greece as the DL537.
Also, in the 1970s GE built the U10A1A for Hedjaz Jordan. This had an extended frame to accommodate the A1A trucks, and was of road-switcher form with the short, low nose that I think was first seen on the U26C. So even though the end-cab form dominated, there were still some-road switchers required here and there.
Inevitably, as part of the scene-setting, this posting has required mention of competing Alco and EMD models, particularly the Alco 6-cylinder locomotives, as these were the most comparable to the GE U9. To complete the worldwide competitive picture, pertinent non-US locomotives in the subject power class might also be considered, particularly those from Alsthom and English Electric. But I don’t think that would add materially to the piece.