Re: United States Potash Railroad

Same general family, but not that close.

The 50 ton (SP 1, SVRR 720) was apparently developed for United Fruit to compete with some similar Whitcombs that United Fruit had bought that used the Cooper-Bessemer EN series engine. It is in effect a downsized 70 ton using the same general arrangement, but different electro-mechanicals. I'm sure foreign customers preferred Cat's world-wide supply chain, and the D397 engine was fairly new.

You might say the 70 ton and its several variations were brothers, but the 50 ton was its half-brother at best. The 50/52/54 tons were all in the same family (brothers) that ended with the early U6B. The next generation was the U5B/U8B, followed by the U6B/U10B and their variations.

The Cooper-Bessemer FWL-6T in the 70 ton line was expanded into the U9B/U9C line and also used as part of UP's last gas-turbines, but then disappeared. GE briefly listed the early U6B in its domestic catalog as a 70 ton replacement with few buyers. The 44 and 70 ton models had both fulfilled their purpose and were just too small as freight cars increased in size and light rail/bridge lines were upgraded or abandoned.