Southern Pacific EMD MP15AC 2754 at Blue Island, Illinois, September 28, 1975, on the Rock Island being delivered. Photographer unknown.

(Craig Garver, Public domain,


GM-EMD blue-white logo.


The EMD MP15AC is a 1,500 hp (1,120 kW) diesel road switcher locomotive built by General Motors' Electro-Motive Division between August 1975 and August 1984. A variant of the EMD MP15DC with an AC/DC transmission, 246 examples were built, including 25 for export to Mexico, and four built in Canada.



The MP15DC's standard Blomberg B trucks were capable of transition and road speeds up to 60 mph (97 km/h), allowing use on road freights. Soon there was a demand for a model with an advanced AC drive system. The MP15AC replaced the MP15DC's DC generator with an alternator producing AC power which is converted to DC for the traction motors with a silicon rectifier. The MP15AC is 1.5 ft (457 mm) longer than an MP15DC, the extra space being needed for the rectifier equipment. The alternator-rectifier combination is more reliable than a generator, and this equipment became the standard for new diesel-electric locomotive designs.

The MP15AC is easily distinguished from the DC models. Instead of the front-mounted radiator intake and belt-driven fan used on all previous EMD switchers, these have intakes on the lower forward nose sides and electric fans. Side intakes allowed the unit to take in cooler air, and the electric fans improved a serious reliability issue found in its earlier DC sisters.


Southern Pacific EMD MP15AC 2730 at Blue Island, Illinois, on the Rock Island, March, 1975, being delivered. Photographer unknown.

"It doesn't get much more "as built" than this ... the lenses aren't even in the lights yet, waiting for the paint to dry." - Craig Garver

(Craig Garver, Public domain,



The MP15 used a roots-blown 12-cylinder 645E engine. The engine is rated at 1,500 hp (1,120 kW). The 645 series, introduced in 1966, was EMD's standard engine through the 1980s.


CP 1422, ex-SOO 1552, and former Milwaukee Road 486.

(Rrshooter, CC BY-SA 4.0 <>, via Wikimedia Commons)


Original owners

The six largest buyers, Milwaukee Road (64), Southern Pacific (58), Seaboard Coast Line Railroad (45), Nacionales de México (25), Long Island (23), and Louisville & Nashville (10), were all buying road locomotives with AR10 alternators throughout the 1970s, so the similarly equipped MP15AC was easily kept in good repair. 36 more units were sold to 8 other customers.


Milwaukee Road EMD MP15AC 464 at St Paul, Minnesota, April 9, 1976. Photographer: Bruce Black.

Milwaukee 464 is part of the second order for 32 units, delivered the previous month, and making the Milwaukee the largest owner of MP15AC's.

(Craig Garver, Public domain,



Type and origin
Power type: Diesel-electric
Builder: General Motors Electro-Motive Division, General Motors Diesel, Canada
Model: MP15AC
Build date: August 1975 – August 1984
Total produced: 246
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Prime mover: EMD 12-645E
Engine type: V12 two-stroke diesel
Displacement: 7,740 cu in (126.8 L)
Cylinders: 12
Cylinder size: 9+1⁄16 in × 10 in (230 mm × 254 mm) bore x stroke
Performance figures
Power output: 1,500 hp (1,120 kW)
Nicknames: "Little Beaver"
Locale: North America