Starting in 1968, GE offered four- and six-axle road switchers with an output of 2,250 hp. They were derived from the U30B and U30C, but had only 12 instead of 16 cylinders. A total of 481 of the four-axle U23B had been built by 1977 when the B23-7 became its successor in the Dash 7 range. The largest customers were the Louisville & Nashville with 90, Penn Cental with 77 and the Southern with 70. The six-axle U23C was built for tasks which required much starting tractive effort, but not much power. From a total of 223, 170 went to the Rede Ferroviária Federal S.A. in Brazil. 150 of these had been built by GE do Brazil. When the Dash 7 was introduced, there was no model with six axles with less than 3,000 hp.