When the AIACR introduced new regulations for 1938 — limiting supercharged engines to 3 litres or unsupercharged engines to 4.5 litres — Auto Union could no longer use its signature V16. The 750 kg minimum weight limit remained, but the capacity restriction forced a fundamental redesign. Dr. Ing. Robert Eberan von Eberhorst took over engineering responsibility for the Type D, replacing Porsche's team as the primary technical authority on the car.
The new V12 engine displaced 3 litres with a supercharger and produced close to 550 hp — similar peak output to the Type C in practice, though with different power characteristics. The engine's smaller size and reduced mass improved its positioning toward the vehicle's center of mass, which substantially reduced the rear-heavy bias that had made the earlier V16 cars so demanding to drive. The Type D was widely regarded as the most tractable of the pre-war Auto Unions.
Rear suspension shifted from the swing-axle system used on the Types A, B, and C to a de Dion arrangement, following an approach Mercedes-Benz had adopted. The front suspension retained parallel trailing arms and torsion bars. These changes combined to make the Type D handle more neutrally than any previous Auto Union, while the V16 engine was retained in hillclimb variants where the capacity limit did not apply.
The 1938 season opened under a cloud: Bernd Rosemeyer, Auto Union's most gifted driver, had been killed in January during a land speed record attempt. His loss left a significant void. The team signed Tazio Nuvolari, already regarded as one of the greatest drivers of the era, and he proved equal to the challenge.
Nuvolari won the Italian Grand Prix and the Donington Grand Prix in 1938, providing Auto Union with its two most significant results of what was otherwise a thin year. The Mercedes-Benz W154, developed in parallel to the new formula, was generally the more competitive package across the season as the two teams each developed their 3-litre designs.
The 1939 season was more fruitful for Auto Union. Nuvolari won the Yugoslav Grand Prix in Belgrade and placed second at the Eifel Grand Prix. Hermann P. Müller won the 1939 French Grand Prix — a notable result — and placed second at the German Grand Prix. Rudolf Hasse managed a second place at the Belgian Grand Prix, and Georg Meier placed second in France. The spread of results across multiple drivers reflected the Type D's improved drivability relative to its predecessors.
Racing ceased with the outbreak of World War II in September 1939.
Three Type D cars are believed to survive today, making them the best-preserved examples of the pre-war Auto Union programme. During the latter stages of World War II, approximately eighteen Auto Union team cars were concealed in a colliery near Zwickau. When Soviet forces captured Zwickau in 1945, the cars were taken as war prizes and distributed to Soviet scientific institutes and manufacturers, including NAMI, for research. Most were eventually scrapped.
American enthusiast Paul Karassik located chassis number 19 in Russia, paired it with an original engine from a separate Type D carcass, and handed it to Crosthwaite and Gardiner for restoration in 1990. A Christie's auction in Paris in February 2007 attempted to sell the car but it did not find a buyer, in part due to discrepancies between chassis and engine numbers. A subsequent Bonhams auction in August 2009 saw bidding reach $6 million without a sale. The three surviving authentic Type D cars represent the largest group of any pre-war Auto Union type to have endured into the present day.
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