Built just before the start of WWII, it is known as the Göttinger Ei (“an egg from Göttingen”) or the Schlörwagen. Its designer, Karl Schlör, a Krauss Maffei engineer, proposed a bodyshell with extremely low drag coefficient as early as of 1936.
A model built at AVA (Aerodynamic testing Institute, Göttingen) was dubbed “tortoise”. During the wind tunnel tests, it showed an anheard-of Cd: 0.113.
The real full-scale car was built on the rear-engine Mercedes-Benz 170H chassis:
With the body built by Ludewig Bros., Essen, the Schlörwagen was also tested in the AVA wind tunnel, Göttingen. Its Cd could not compare to the model’s but still was remarkably low: about 0.18.
In 1939, the Egg was presented to the public. It was the star of Berlin Auto Show.
During the war, the project was mothballed.
But Herr Schlör succeded in testing his car in the aeromobile role, with Soviet M-11 135hp engine installed.
The fate of the Schlörwagen is unclear. Some sources say it was taken to Britain. No proof, though. Its inventor died in 1997.
Sources: Google Groups, Aptera Forum