The GE AC44C6M is an AC-traction 4,400-horsepower (3,300 kW) diesel locomotive, rebuilt from GE Transportation Dash 9 locomotives. AC44C6M rebuilds have been done by GE (now Wabtec), American Motive Power, Inc., and Norfolk Southern Railway's Juniata and Roanoke Shops, starting in September 2015. The AC44C6M retains the 16-cylinder 7FDL-16 prime mover used in the core locomotive prior to rebuilding, but replaces the Dash 9's DC traction motors with alternating current GE 5GEB13B7 traction motors. Externally, the rebuilds have received new wide-nosed cabs, a new front hood section, and a new inverter cabinet behind the cab, while retaining the underframe and engine and radiator compartments of the original Dash 9 units.

Rebuilding an old Dash 9 locomotive into an AC44C6M costs only 50-60% that of purchasing a brand new AC locomotive.^[3] Wabtec claims a 17% improvement in fuel efficiency, 30% improvement in reliability, and a 55% improvement in haulage capability.^[4]

BNSF was the first railroad to order locomotive rebuilds with an order for 20 AC44C4Ms that were delivered in September 2015.^[5][6] The AC44C4M is a similar to the AC44C6M, but AC44C4M locomotives feature 4 traction motors and an A1A-A1A configuration rather than the AC44C6M's 6-traction motors in a C-C configuration. This is similar to the ES44C4 and ET44C4 that BNSF also operates. These locomotives also retain their original cabs. BNSF has so far been the only customer of the AC44C4M.

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.^[7] Norfolk Southern is the largest operator of the AC44C6M, with over 600 locomotives rebuilt as of 2022, and a further 330 by 2025.^[8] 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).^[9][10]

Quebec North Shore and Labrador Railway has 19 AC44C6M locomotives. These were rebuilt from former BNSF Dash 9 locomotives.^[11]

Fortescue Metals Group has 28 AC44C6M locomotives. These feature a larger radiator than other AC44C6M rebuilds.^[12]

Union Pacific also announced plans to rebuild 75 of their Dash 9 locomotives into AC locomotives, presumably AC44C6Ms, as part of a large order to rebuild much of their GE locomotive fleet ^[13] 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.

A Canadian National AC44C6M rebuild was spotted outside of a Wabtec facility in early September 2022.^[14] This was later revealed to be an order for 50.^[15] 60 more units were ordered in 2023 for a total of 110.^[16]

The AC4400CWM is a similar rebuild program undertaken by GE/Wabtec, but starts with an AC4400CW and AC6000CW (UP only) instead of a Dash 9. Union Pacific, CSX, and CPKC have rebuilt several hundred AC4400CW into AC4400CWM models.

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