Alco-GE was a partnership between the American Locomotive Company and General Electric that lasted from 1940 to 1953. Their main competitor was EMD. Under this arrangement, Alco produced the locomotive body and prime mover, and GE supplied the electrical gear. Alco management could see that the market for steam locomotives would soon vanish, and General Electric was interested in getting into the lucrative diesel locomotive market.
GE later dissolved the partnership and decided to build their own locomotives. Alco still received electrical gear from GE, but was no longer GE's sole customer for such parts. The first diesel road locomotives GE built were two A-B sets, later called the UM20. GE's first production domestic road locomotive was the U25.