General Electric U6B s/n 33494 shipped from GE 5-27-1959 new to Santa Maria Valley - weight 70 tons Caterpillar D397D turbocharged engine 700/640hp. Was not used in the lead often since crews did not like its close clearance cab. Reported to have cracked heads in 1998, scrapped and parts salvaged. I heard a few years ago a locomotive dealer still had the main generator. I'm not sure why SMV bought this as there were some standard GE 70 tons on the used market in this era.

s/n 33493 was apparently loaned to Lancaster and Chester while their standard GE 70 tons took trips back to GE for rebuilding. After a year, it's odd prototype swing-bolster trucks were exchanged for 42" gauge standard trucks and resold to Manila Railroad.

It has been claimed that the U6B was intended as a replacement for the GE 70 ton, but this isn't really the case. The last GE 70 tons for US use were built in early 1957, though production continued with a slightly different body styles and newer traction motor until late 1958/early 1959 for export customers.

In 1952 GE produced a narrow gauge "50 ton" design for several subsidiaries of the United Fruit Company ("Chiquita") for use in Central America and the Caribbean. This was a smaller version of the 70 ton design, but used the new Caterpillar D397 supercharged engine rated at 450/400 hp. This design was apparently to compete with Whitcomb (which delivered its last locomotive that year but production continued a few more years under parent BLH) that had previously delivered a similar design to United Fruit that used a Cooper-Bessemer EN series engine. The only one of this model delivered in North America was Southern Pacific #1 that worked the narrow gauge in the Owens Valley from 1954-1960 before being resold to a copper mine in Mexico. There was also a similar 52 ton model. All of these were 36" or 42" gauge except for SP #1 (36" gauge but designed to be changed to standard gauge which it eventually was) and four 52 tons in Venezuela built as standard gauge. The last order for these were built in 1957, including one for United Fruit.

In 1956 after its joint marketing agreement with Alco expired, GE began advertising its new Universal Line of locomotives including the U4B, U6B, U9B, U9C, U12B, U12C, U18B, U18C, UD18B. These were primarily intended for the export market (except for the UD18B of which some were built for NdeM) and all were capable of narrow gauge except the U18B/UD18B. The U9B/C used an upgraded Cooper Bessemer 6 cylinder engine like the GE 70 ton, but now rated at 990/900 hp. The U9/12/18 were all roadswitcher types using Cooper Bessemer engines while the U4B and U6B were end cabs with Caterpillar engines intended to replace the 50/52 ton design.

The 1956 advertised U4B/U6B were never produced, but in 1956 US Gypsum's Plaster City operation did receive two modified 54 tons of this design. Its not clear if GE simply adopted the USG design for their Universal model or the USG units were the first Universal end cabs. There are drawings for a second U6B design circa 1957/58, again never built. The U4B model was apparently abandoned.

Finally in 1959 the first actual production U6B units (third version) were built including the L&C/Manila and SMV units, using a different design compared to the 1956 advertised model. It did see some reasonable success, though I'm not sure any are left in service.

The U6B was replaced in 1961 when Caterpillar discontinued its D397 engine line with the Cat D398 powered U8B, and U4B successor U5B using the Cat D379 engine (V8 version of the D398 V12) using a newer carbody. About this time GE had assumed production of the Cooper-Bessemer engine and the rest of the line was upgraded to U10/U13/U20 using the I6/V8/V12 engines. Two oddballs were U8B units in older U6B(III) carbodies for Hampton & Branchville, long out of service and now reported to have been scrapped.

By 1965 Cat had upgraded their engines and GE offered the U10B (the Cooper-Bessemer version was never built marking the end of the 6-cylinder engine but GE did continue to build replacement prime movers) and the U6B (4th version). In the early 1990s, Cat had discontinued the D398/D379 so the very last orders of the U10B/U6B were built using the Cat 3512/3508 engines. This version of the U6B was very popular, and the majority of them remain in daily service around the world.

So a GE U6B can be one of five distinct designs designated as such, only the last three actually produced, from 24" gauge (UM6B modified South African design) to broad gauge over a period of 30 years. Some export customers that had previously bought the 70 ton did buy the later end-cab Universals, but the U4B/U6B(I) were really the replacement models for the 50/52 ton export design. By 1960 there wasn't much of a market left for new GE 70 tons that could run on 60 pound rail and cross E40 bridges. What demand existed could be filled by the used locomotive market as previous owners either upgraded or abandoned.

It is somewhat strange that there weren't any of the Universal end cabs sold in North America beyond the one for SMV and two for H&B though GE seemed to have no problem selling center cabs of similar size until demand ended for anything in this size/hp range. In addition, there were several GE licensees that also built some of these designs around the world.