In the summer of 1960, EMD's sales team got an unpleasant surprise. General Electric, which had divorced partner Alco in 1953 and was thought to be making only export diesels, had suddenly fielded an American road switcher. Worse yet, GE's upstart U25B, regarded today as the first of the second-generation diesels, was more powerful, more modern, and required less maintenance than EMD's flagship offering, the GP20. Perhaps fortunately for EMD, the railroad industry was in a slump at the time; as the designers at La Grange rushed a competitve model into production, not a single U-boat was sold that first year.
To create a new engine in a short time frame, EMD's designers borrowed the frame and trucks from the GP20 and uprated its 2000 hp 567 diesel to 2250 hp - still 250 hp short of the U25B. They also borrowed one of the U25B's most revolutionary features: a centralized air cooling system with a self-cleaning filter that pressurized the engine room to keep out dust and dirt. This replaced the myriad air filters in older diesels and significantly reduced maintenance.
To fit the pressurized air system and other upgrades into the existing GP20 frame, the only place to go was up. EMD stacked the air system, turbocharger and electrical gear behind the cab, and a higher carbody was needed, giving the new engine a unique profile not seen before or since in the EMD lineup. For styling assistance, EMD turned to the GM Automotive Styling Center in Troy MI. The result was a unique cab roof profile and a characteristic rooftop hump, to house the intakes for the central air system and dynamic brake cooling.
According to EMD's normal naming practice, the new engine should have been called the GP22 - but that hardly sounded competitive with the U25B. So the marketing department dubbed the new model the GP30, claiming it had 30 distinct improvements over the GP20.
In fact, the GP30 turned out to be an excellent locomotive. During a production run of just over two years, from July 1961-November 1963, 948 units were sold to railroads across America, nearly double the quantity of U25Bs sold during six years of production. Although slightly less powerful, the Geep was a known quantity, with an engine and other parts familiar to virtually every railroad's maintenance department. Advertised by EMD as a combination "high speed and heavy drag" locomotive, the GP30 immediately took over from first generation diesels as premier mainline freight power. Although bumped to lesser service by more powerful engines later in life, many served over four decades, considerably longer than the expected service life of a diesel. Some railroads, like the Burlington Northern and Chessie System, operated rebuild programs that upgraded old GP30s to higher specs and kept them running late into the 20th century.