The ALCO RSD-12 was a C-C diesel-electric locomotive rated at 1,800 horsepower (1.34 MW).

They were used in much the same manner as its four-axle counterpart, the ALCO RS-11, although the six-motor design allowed for better tractive effort at lower speeds.

• Nickel Plate Road #329 is preserved at a museum in Bellevue, Ohio.

• Paperton Junction Southern (ex-SP #2962) is preserved at the Arkansas Railroad Museum in Pine Bluff, Arkansas.

• Lake Superior & Ishpeming #1804 partially survives in a shipyard in Escanaba, Michigan.