The EMD MP15AC is a 1,500 hp (1,120 kW) dieselswitcher/road-switcherlocomotive built by General Motors' Electro-Motive Division between August 1975 and August 1984. 246 examples were built, including 25 for export to Mexico, and four built in Canada. The MP15AC was a development of the earlier MP15DC model, but replaced the earlier model's DCgenerator 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 its predecessor. 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.
Railroads that originally bought MP15ACs were the Southern Pacific, Missouri-Kansas-Texas (MKT), TFM, Conrail, Long Island Rail Road (LIRR), and the Milwaukee Road. Former Milwaukee Road units are now owned by the Soo Line Railroad (an American operating subsidiary of the Canadian Pacific Railway); those not painted in the Canadian "Golden Beaver" scheme have worn a Soo Line patch job; those wearing it are often called "Bandits".
Six former Milwaukee units returned to "home rails" in 2008, serving the growing regional Wisconsin & Southern Railroad WSOR in Milwaukee, Madison, and Horicon. In addition, Union Pacific has bought many examples on the used locomotive market. The New York & Atlantic Railway, which carries freight on Long Island, uses 4 former Long Island Railroad MP15ACs to haul freight along with other ex LIRR locomotives.
