EMD SW900

The EMD SW900 was a diesel switcher locomotive produced by General Motors Electro-Motive Division beginning in late 1953, serving as the successor to the SW8 in EMD's catalog. The model designation reflected a shift in EMD's naming conventions toward a horsepower-based system, with the number directly indicating the locomotive's rated output. Production continued through the mid-1960s for domestic American customers, with Canadian output from General Motors Diesel extending several years beyond that. In total, the type achieved a respectable production run, with American railroads accounting for the largest share of orders, followed by substantial Canadian purchases and a smaller number of export units delivered to mining operations in Venezuela, Peru, and Liberia. The SW900 found work across a wide variety of switching assignments on American and Canadian railroads during the 1950s and 1960s, where its modest power output was well suited to yard switching and light industrial duties. An unusual episode in the model's history involved the Reading Company, which in the early 1960s contracted with EMD to have fourteen of its Baldwin VO 1000 switchers rebuilt to SW900 mechanical specifications, though these units retained their original Baldwin carbodies and were rated by EMD at 1,000 horsepower. Southern Pacific Transportation Company undertook a different kind of rebuild program in 1974, sending ten of its SW900s to the railroad's Houston Shops for comprehensive upgrades that significantly extended their working lives. The SW900's legacy includes a modest but notable set of variants and derivatives. EMD cataloged a cow-and-calf configuration designated the TR9, though no examples were ever ordered or constructed. Some units were assembled using electrical generators salvaged from traded-in older EMC switchers originally powered by Winton engines, and these locomotives were internally classified as SW900M, though their actual output was reduced compared to a standard SW900 due to the older generating equipment. The final examples built by General Motors Diesel in Canada were equipped with updated prime movers rather than the original 567C engine, marking a quiet technological transition at the very end of the model's production life.

The SW900 was powered by an EMD 567C prime mover in eight-cylinder configuration, producing 900 horsepower and driving the locomotive through a direct current electrical transmission system. The B-B wheel arrangement, meaning two two-axle trucks, was standard for the type and consistent with EMD's switcher practice of the era. A single exhaust stack distinguished the SW900 visually from some contemporaries, and the model was built concurrently alongside the twelve-cylinder SW1200, the two designs sharing a common lineage while differing primarily in engine displacement and output. The SW900M variants, assembled with generators from older traded-in switchers, delivered only 600 or 660 horsepower depending on the specific generator installed, making them meaningfully less capable than a standard SW900 despite sharing the same basic platform. Southern Pacific's 1974 Houston Shops rebuild program demonstrated the adaptability of the basic SW900 structure. Those ten rebuilt units received twelve-cylinder EMD 645E prime movers in place of the original eight-cylinder 567C engines, raising horsepower from 900 to 1,200. The program also included a fully updated electrical system encompassing a new generator, replacement traction motors, and a modernized control arrangement. In a similar vein, the last two SW900s completed by General Motors Diesel in Canada were factory-equipped with eight-cylinder 645E engines rated at 1,000 horsepower, illustrating how the 645 series engine had matured into a direct replacement for the older 567 family by the close of the model's production run.