General Electric’s “Dash 7” locomotive line was introduced as a replacement for the older “Universal-Series” of the 60s and early 70s. “Dash 7” series improvements included increased fuel efficiency, tractive effort and reliability. The B23-7 was a direct replacement for the 2,250HP U23B model. The first units were produced for Conrail in September, 1977 (ironically, 3 months after the last U23B was delivered to Conrail). Production continued through 1984, with a total of 535 units built. Conrail was the largest purchaser of the model, with a total fleet of 141 units.
Several features distinguished B23-7s from predecessor models. The long hood stepped outward in the area of the exhaust stack to accommodate a relocated oil cooler. In addition, the frame was 2 feet longer than that of the U23B. An FB-2 style truck was offered as standard equipment on B23-7s, but some railroads opted to use “trade-in” trucks. Therefore, AAR type B and Blomberg trucks could be found on some models. The six power assembly doors (located near the center of the long hood) indicated that the B23-7 was powered by a 12-cylinder GE FDL engine.
There were three distinct “phases” of GE 4-axle “Dash 7” locomotive production. Models on this run represent both “phase 1” and "phase 2" units. Phase 1 units feature a 36’2” wheel base and were built through the Spring of 1979. Phase 2 units feature a 37' 2" wheel base, and production lasted from the Spring of 1979 through the Fall of 1980.