To satisfy railroad interest in a locomotive of intermediate horsepower, General Electric slipped a 12-cylinder FDL-12 into the carbody of the U30B, producing the U23B model. The same modification was used to produce the U23C from the U30C. The generally accepted spotting feature/difference between a 12-cylinder and a 16-cylinder equipped Universal series locomotive is the number of tall carbody doors, which correspond to the number of cylinders per side: a 12-cylinder locomotive has six tall engine room doors per side, a 16-cylinder locomotive has eight tall doors per side, one at each cylinder location. Production ran from August 1968 through June 1977. Conrail bought ten U23B's, the last ones produced, in May-June 1977, road numbers 2789-2798. All told, GE produced 425 USA, 40 Mexican, and 16 export copies of the U23B. This particular locomotive went on to the Providence & Worchester, becoming 2204, and lasted until 2002-2003 before being traded for ex-LMX B39-8's.

It is seen here in the company of two MP SD40-2's (3246 and 3282) at the east end of the former CB&Q, and by this photo date, BN yard in Cicero, Illinois. It will be routed to an empty arrival track, cut off its train, run around the yard back to the east end, and pick up a newly sorted train fresh off the hump, and drag it back (as a trailing unit) to home rails.