The EMD SW1200 is a diesel switcher locomotive built by General Motors Electro-Motive Division between January 1954 and May 1966. Power was provided by an EMD 567C 12-cylinder engine which generated 1,200 hp (895 kW). Late SW1200s built in 1966 were built with the 567E 12-cylinder engine. Additional SW1200 production was completed by General Motors Diesel (EMC) in London, Ontario, Canada between September 1955 and June 1964.
737 examples of this locomotive model were built for American railroads, 287 were built for Canadian railroads 4 were built for Brazilian Railroads, 25 were built for a Chilean Industrial firm, and 3 were built for the Panama Canal Railway.
A cow-calf variation, the TR12, was cataloged, but none were built.
A few units were built with dynamic brakes, featuring large square box with a fan on top of the hood, right in front of the cab.
An SW1200RS is a variant of the standard SW1200, having large front and rear numberboards on some units, EMD Flexicoil-B trucks, and larger fuel tanks for road service. The majority of the Canadian National and Canadian Pacific SW1200 fleets were SW1200RS variants.
Many are still in use today, parts are still readily available and considering their low running cost and high reliability it looks like they will continue to be used for the
These locos are capable of producing 1200hp, hence SW1200; most were fitted with EMD#AARA trucks for shunting duty, however the SW1200R submodel was fitted with EMD#BlombergB trucks for mainline duty. They are typically fitted with the EMD 12c567ci engine, excepting 9 units which had a single phase electric pantograph for OHLE duty, instead of the onboard diesel engine.
Source: Locomotive Wiki