The GE Evolution Series ES44AC locomotive represents an incredible combination of power, performance and efficiency. Originally designed to meet US EPA Tier 2 emissions, the ES44AC locomotive utilizes a 12-cylinder GE Evolution Series engine with 4-stroke combustion technology to maintain horsepower, reduce emissions, and lower fuel consumption compared to GE’s predecessor 16-cylinder FDL engine. From 2005 to 2015, the ES44AC became GE’s standard North American locomotive and a compelling platform for others worldwide. All North American Evolution Series locomotives are equipped with Nathan-Airchime K5HL-R2 "Evolution" airhorns, and later models are equipped with a Graham-White 373 Electronic Bell.

The Evolution Series was named as one of the "10 Locomotives That Changed Railroading" by Trains Magazine. It was the only locomotive introduced after 1972 to be included in that list. The Evolution Series are some of the best-selling and most successful freight locomotives in United States history.

The ES44AC (Evolution Series, 4400 HP, AC Traction) replaced the AC4400CW model in the GE catalog. Every Class 1 railroad in North America has ordered these locomotives. Even shortlines such as Iowa Interstate ordered them to handle traffic growth from new ethanol plants. 100 lease units were acquired by Citirail/CREX for use as lease units by the class 1 railroads if their own locomotive(s) needed to spend time in the shop.

The Intermountain ES44AC faithfully reproduces the prototype, painting and details are specific to the road name and, in some cases, the road number. The model features many separately applied brass wire, etched metal, and plastic details. All are Ready-to-Run. Some details may be included for installation by the modeler.