An SD39 is a 6-axle diesel-electric locomotive built by General Motors Electro-Motive Division between August 1968 and May 1970. 54 were built for American railroads.
In 1966 EMD replaced all their old models with new ones having the new 645 diesel. These included six-axle models SD38, SD40, SDP40 and SD45; the SD39 was added in 1968. All shared standard components including the frame, cab, traction alternator, trucks, traction motors, and air brakes. The difference was the power output: SD38 = 2,000 hp (1,490 kW) from a non-turbocharged V16, SD39 = 2,300 hp (1,720 kW) from a turbocharged V12, SD40 = 3,000 hp (2,240 kW) from a turbocharged V16, and SD45 = 3,600 hp (2,680 kW) from a turbocharged V20. The SD39 had the smallest prime mover and therefore had the most unused space above the frame, inside the hood between the main generator and electrical cabinet, and outside in large end "porches".
A variant was the SDL39, ordered by the Milwaukee Road. Shorter and lighter than a stock SD39, these minimized weight per axle.
Original owners 
Dash 2 Rebuilds 
On January 1, 1972 EMD debuted Dash 2 models. No SD39-2s were built as new units, but a number SD39s were rebuilt to Dash 2 specifications.
- Pinkepank, Jerry A. (1973). The Second Diesel Spotter’s Guide. Milwaukee, WI: Kalmbach Publishing Company. ISBN 0-89024-026-4.
- Trains Magazine Article December 1968, "A Market Oriented Catalog" by Wallace A. Abbey. The same article appears in Kalmbach's Our GM Scrapbook pages 82–83 subtitle, "Little diesel, big job".