EMD MP

EMD MP
Name	EMD MP
Powertype	Diesel-electric
Builder	Electro-Motive Division
Builddate	1950s–1960s
Totalproduction	Various
Wheelarrangement	B-B, A1A-A1A
Prime mover	EMD 567 and 645 series
Transmission	Electric
Tractiveeffort	Varies by model

EMD MP The EMD MP series comprises a family of medium-power road switcher and passenger diesel-electric locomotives produced by Electro-Motive Division for North American and international railroads. These locomotives combined features derived from earlier EMD F-unit freight cab designs and EMD GP road-switcher developments to serve secondary mainline, branchline, and passenger assignments. Introduced during the postwar dieselization era, the line influenced roster standardization among carriers such as Atchison, Topeka and Santa Fe Railway, New York Central Railroad, and export customers in Mexico and Argentina.

Introduction

The MP series was marketed to railroads seeking intermediate horsepower between switchers and high-horsepower road units, competing in a market alongside models from General Electric (company) and Alco. Early development responded to operational needs voiced by carriers including Union Pacific Railroad and Pennsylvania Railroad for versatile locomotives capable of both freight and passenger service. The MP family incorporated components like the EMD 567 prime mover, Blomberg trucks on some variants, and optional steam generators or HEP for passenger service, aligning with the practices of Santa Fe and Southern Pacific Transportation Company.

Design and Development

Design work at Electro-Motive Division during the late 1940s and 1950s produced a transitional platform linking the aesthetics of the EMD F7 with the modularity of the EMD GP7. Styling cues and carbody construction used techniques developed at General Motors subsidiaries, and the MP frames accommodated different truck arrangements—B-B for high adhesion and A1A-A1A for lighter axle load applications used by carriers such as Canadian National Railway and British Rail exportesque buyers. The development program reflected lessons from unitized designs delivered to Chicago and North Western Railway and Missouri Pacific Railroad, with input from road managers at Chicago, Burlington and Quincy Railroad and maintenance staffs at Baltimore and Ohio Railroad.

Engineering changes across model years included revisions to cooling systems, electrical cabinets manufactured to specifications influenced by Westinghouse Electric Company practices, and the introduction of modular cab components shared with the EMD SD series. Negotiations with procurement officers at New Haven Railroad and Rock Island Line shaped optional fittings such as multiple-unit (MU) control compatibility and dynamic braking, features also requested by Great Northern Railway and Northern Pacific Railway.

Engines and Mechanical Specifications

Most MP models were powered by variants of the EMD 567 two-stroke diesel engine, later superseded in some models by the EMD 645 family to increase displacement and reliability. Electrical transmission used DC generators and traction motors supplied under license or contract with manufacturers like General Electrical Company and Westinghouse Electric Company. Truck designs ranged from Blomberg B trucks to AAR-design trucks, similar to those fitted to EMD GP9 and EMD F9 units; axles and suspension systems reflected practices validated on Penn Central and Seaboard Air Line Railroad rosters. Brake systems followed AAR standards and could include straight air, independent, and automatic freight braking compatible with Association of American Railroads protocols.

Auxiliary systems offered options for steam generators to heat passenger consists—specifications often mirrored equipment used by Amtrak successor services and pre-Amtrak carriers such as New York, New Haven and Hartford Railroad. Electrical head-end power (HEP) retrofits matched standards later adopted by Conrail and commuter rail agencies including Metra.

Models and Variants

The family encompassed multiple designations reflecting horsepower, truck arrangement, and service role. Examples paralleled the approach taken for models like the EMD GP18 and EMD SD24 where suffixes denoted modifications; variants included road-switcher MP units for freight, passenger-equipped MPs with steam generators, and export versions customized for gauges and clearances of Brazil and Chile. On some railroads, rebuild programs produced hybrid units akin to remanufactured fleets seen on Southern Railway and Illinois Central, with updates to traction motors and control systems comparable to conversions of EMD GP9 units.

Custom orders produced units with specific coupler, radio, and signal equipment to meet the needs of operators such as Kansas City Southern, Union Pacific, and regional carriers in Mexico and Peru.

Service History and Operators

MP units served widely across North America with operators including Santa Fe, Union Pacific Railroad, Canadian Pacific Railway, Canadian National Railway, Illinois Central, and Southern Pacific Transportation Company. They performed local freight, road-switcher duties, and secondary passenger services, often replacing steam-era locomotives on branchlines in the 1950s and 1960s. Export sales placed units on the rosters of Ferrocarriles Argentinos, Ferrocarriles Nacionales de México, and industrial operators associated with Cargill and mining firms in Chile.

During the consolidation era, units were absorbed into fleets of Conrail and later shortline operators spun off by companies such as Genesee & Wyoming Inc.. Rebuilds and retirements paralleled trends affecting contemporaries like Alco RS-3 and Fairbanks-Morse units, with many MPs seeing service life extensions via overhauls undertaken by shops linked with ATSF and regional maintenance contractors.

Preservation and Surviving Units

A number of MP-series units survive in museum and tourist railroad collections, maintained by organizations such as the California State Railroad Museum, Illinois Railway Museum, and regional preservation groups tied to former operators like Santa Fe and Southern Pacific. Preserved examples often appear at heritage rail excursions alongside contemporaries like EMD F7 and GP9 units, and restoration projects sometimes incorporate replacement parts patterned after EMD 567 and EMD 645 engines sourced from commercial suppliers used by Amtrak shops. Heritage operations have displayed units during events connected to anniversaries of companies such as Atchison, Topeka and Santa Fe Railway and historical societies in Illinois, California, and Texas.

Category:Diesel-electric locomotives