Powered by a V12 FDL prime mover, the 2250 h.p. U23B was GE's intermediate-sized four-axle road-switcher of the late 1960s through the mid 1970s. The U23B's direct competitor during this period was the very successful EMD GP38. In 10 years of production, from 1968 through 1977, a total of 481 units were produced, making this the second best seller of GE's "Universal Series" locomotives. The first units were delivered to the Delaware & Hudson in August and September 1968. CSX predecessors Chesapeake & Ohio and Louisville & Nashville had a combined fleet of 120 units, giving CSX one of the larger active fleets in later years. Penn Central, Santa Fe and Missouri Pacific also purchased sizeable fleets of U23Bs.