BNSF was the first railroad to order locomotive rebuilds with an order for 21 AC44C4Ms that were delivered in September 2015. These were followed shortly by Norfolk Southern's AC44C6M's, which were first delivered at the end of 2015, and rebuilt from their
Dash 9-40C locomotives. Norfolk Southern is the largest operator of the AC44C6M, with over 600 locomotives rebuilt as of 2022, and a further 330 by 2025. All of their Dash 9-40C units, and significant numbers of their
Dash 9-40CW units have been rebuilt into AC44C6Ms. The railway plans to rebuild all of its remaining Dash 9–40CW units into AC44C6Ms. Norfolk Southern's AC44C6M locomotive features a new under-floor air conditioner, cab signals, LSL (Locomotive Speed Limiter),
DPU systems,
PTC, and
ECP braking ability (on some units).
Quebec North Shore and Labrador Railway has 19 AC44C6M locomotives. These were rebuilt from former BNSF Dash 9 locomotives. As at October 2024,
Fortescue has 28 AC44C6Ms. These feature a larger radiator than other AC44C6M rebuilds.
Union Pacific also announced plans to rebuild 75 of its Dash 9 locomotives into AC locomotives, presumably AC44C6Ms, as part of a large order to rebuild much of their GE locomotive fleet. Union Pacific is a major customer of the similar AC4400CWM rebuild program. All of these locomotives are classified as C44ACM, which is similar to the
C60AC (including convertibles) and
C44AC rebuilds. All of the rebuilds use UP's new paint scheme that was introduced in late 2022.
Canadian National ordered 50 AC44C6Ms, and received the first one in October 2022. 60 more units were ordered in 2023 for a total of 110. In 2025, 11 more units were ordered, raising the total to 121.
CSX announced in February 2026 that Wabtec would rebuild 50 Dash 9 locomotives and convert them from DC to AC traction. ==Similar rebuilds==