With the advent of diesel traction in various areas of application in the USA, more and more diesel-powered shunting locomotives were procured. In the mid-range, the problem lay in a law requiring a second person in the cab to play the role of fireman for locomotives of all types of propulsion weighing 90,000 pounds and over. As a result, several manufacturers developed diesel shunters just below this limit, of which the 44-tonner from GE was the most well-known model.

In order to ensure an optimal view in both directions of travel, the driver's cab was placed exactly in the middle and raised. There was a hood on each side of the driver's cab, under which was a diesel engine with a generator. Most of the locomotives were powered by two Caterpillar D17000s with eight V-shaped cylinders and 180 hp each. With a maximum of ten pieces each, different six-cylinders were used. This was either the Hercules DFXD also with 180 hp, the Buda 6DH1742 with 200 hp or the Caterpillar D342 with 190 hp. 

Of a total of 386 built vehicles, 276 went to US companies. 47 pieces were created from a special military variant that were delivered to the US armed forces. These had been given a lower cab for use in Europe and weighed down to 90,000 pounds. Of these, 31 were later sold to the Indian Railways and twelve to the Portuguese CP. The remaining four went to Australia, where they first came to the New South Wales State Railways and were listed as Class 79s. They changed hands several times and two of them ended up with the British Phosphate Commission where they were fitted with more modern Caterpillar D3306 engines in 1979.

With the Dash 9 generation, General Electric skipped the option to offer four-axle road switchers and only offered six-axle locomotives. The first model introduced in 1993 was the Dash 9-44CW, officially called C44-9W. So it basically was a modernized successor of the Dash 8-44CW, meaning it has 4,400 hp, the C-C wheel arrangement and a wide nose. With this generation, the wide nose could be found on the vast majority of locomotives built.

Power still came from the proven 7FDL16 engine that had been in use for decades. While this locomotive had DC traction motors, the AC4000CW was offered with three-phase AC traction motors. As many railway companies were still sceptical about the new type of traction, the Dash 9-44CW could find more customers than its AC counterpart. By 2004 when the Evolution series had been introduced, GE had built 3,668.

For the EPA Tier 2 emissions standard, GE developed the new Evolution Series engine, also known as “GEVO”. By far the most successful variant, with almost 3,900 locomotives sold, is the ES44AC, the successor to the AC4400CW with three-phase traction motors. The Union Pacific is the largest operator with 1,234 locomotives, of which 296 are ES44AH with heavier weight of 432,000 pounds. For customers who still preferred DC powered locos, the 4,000 hp ES40DC and 4,400 hp ES44DC were offered. For Australian customers, the ES44ACi and ES44DCi were offered, which have better cooling.