The U18B and U18C are four- and six-axle road switchers built by General Electric from 1956. All are being powered by an eight-cylinder 7FDL delivering 1,800 hp for traction. Originally, only the U18C was built for export. Depending on the customer, they had a weight between 84 and nearly 100 tonnes that was spread over six axles to reduce the axle load. The type was offered in various gauges between three feet (914 mm) and five and a half feet (1,676 mm). While the older batches had a high nose, the newer ones got a low one.

The largest customer of the U18C was Indonesia where the class was designated CC201. 92 were directly built with a C-C wheel arrangement, while 52 more were rebuilt from class BB203 A1A-A1A locomotives. On South Sumatra, some were later rebuilt with slanted cabs like the ones on newer CC203 and CC204. From a total of 246 U18C, 45 went to Nigeria, 36 to Argentina, 29 to Columbia and 25 to Algeria. Among the locomotives for Columbia, 21 which had been ordered by Drummond Coal were built by GE do Brasil between 1994 and 2001.

A variant of the U18C was the U18C1 that had an additional leading axle in each bogie. It was built 115 times for South Africa and designated class 32-000. The four-axle U18B only appeared in 1973 and was mainly intended for the domestic market. GE's goal was to offer a light branch line locomotive that was the only one in the North America with the company's eight-cylinder prime mover. It was no great success with 118 for US customers, of which 105 went to the Seaboard Coast Line, and 45 for the Ferrocarriles Nacionales de México. A similar four-axle variant was the UD18B that had been built as a switcher for Mexico that had already been built in 1956.