German Professor, Wunibald Kamm worked with aerodynamics engineer Baron Reinhard von Koenig-Fachsenfeld. They developed a design with a smooth roofline and a taper in the automobile's body that is suddenly chopped off at the rear end. This design makes the air flow act as if a full tapered "tail" was present on the vehicle. A full size prototype was developed in 1938. It was a four-door sedan featuring a sharply truncated rear end. The test car represented a compromise between a low air resistance and practicality in the automobile's size and shape.