EMD SD24

Technical Specifics

The EMD SD24 was introduced in July 1958 as the product of Electro-Motive Division's effort to bring turbocharged power to its six-axle road switcher line. Built at EMD's La Grange, Illinois facility, the SD24 holds the distinction of being the first EMD production locomotive to incorporate a turbocharged diesel engine, entering production roughly sixteen months before the four-axle GP20 followed suit. EMD initially anticipated strong interest from the Duluth, Missabe and Iron Range Railway, going so far as to paint the first demonstrator unit in that road's colors, but the DMIR ultimately declined to purchase the type and the demonstrator was instead delivered to the Union Pacific Railroad. A total of 224 units were constructed between 1958 and March 1963, of which 179 were conventional cab-equipped locomotives and 45 were cabless B units built exclusively for Union Pacific. Sales of the SD24 proved only moderately successful by EMD's standards, though the locomotive served on several prominent railroads. The Atchison, Topeka and Santa Fe Railway was among the largest customers, eventually accumulating a fleet of eighty units. As the locomotives aged through the 1970s, reliability concerns emerged, particularly involving electrical systems, and the added maintenance demands of the turbocharged powerplant became difficult to justify in secondary service. This prompted a wave of rebuilding programs by various owners. The Santa Fe undertook the most extensive effort, rebuilding its entire SD24 fleet between January 1973 and January 1978 into what the railroad designated the SD26, upgrading the prime movers with EMD 645 power assemblies and replacing the electrical systems wholesale. The Illinois Central Gulf Railroad pursued a different approach, rebuilding a mixture of SD24s alongside other C-C locomotives into 2,000-horsepower SD20s between 1979 and 1982, removing the turbocharger and upgrading the electronics to Dash 2 standards. Union Pacific experimented with three individual units to evaluate potential fleet-wide upgrades, though none of these experimental modifications were ultimately replicated across the broader roster. Despite its modest commercial performance, the SD24 occupies an important place in diesel locomotive history. Its introduction of EMD's mechanically assisted turbo-compressor established the foundation for all subsequent turbocharged EMD products and set the developmental course that led to the high-horsepower six-axle locomotives that came to dominate North American railroading in later decades. One SD24 was acquired by Kennecott Utah Copper for industrial service, representing the lone example ordered outside of general railroad use.

Prototype Reference

Real-world information about this equipment type