"One morning," Flettner writes, "while lying in the sand, I tried to explain to my wife the meaning of the Magnus Effect. I attempted to explain its peculiar action by rolling grains of sand from a little sand hill, and making them at the same time pass my fist which I turned in the moving sand. One could clearly see that on the side of the fist where the direction of rotation coincided with the direction of the moving sand, the grains moved very much faster; while on the opposite side they came to a standstill. . . . . During the following night I could not sleep a wink. In those few hours I fought a battle with myself which later for months I had to fight with all the experts. . . . . I was asking myself whether I should take it upon myself to introduce along my rudder system also the rotating sail, which seemed to be really revolutionary."

On 16th September, 1922, Anton Flettner applied for a German patent for the Rotor ship. Flettner's first idea was to create the propelling force needed by means of a belt moving around two cylinders: he thought (wrongly) that, in this way, a much greater circulation would be maintained. But, after several months of further thought, the belt-idea was abandoned, and the Rotor-ship concept emerged.

With the support of Betz, Ackeret and Prandtl, he was able to build an experimental rotorboat, and by October, 1924, the Germania Werft completed the construction of a large two-rotor ship under the name Bruckau. After successful conclusion of the trials, in February 1925, the Bruckau started on her first voyage from Danzig across the North sea to Scotland. The voyage was a complete success. In stormy weather the rotors did not give the slightest trouble. The return trip was equally successful, and the two trips proved conclusively that the rotorship could sail into the wind at about 20 to 30 degrees. On 31st March, 1926, now under the name Baden Baden the rotorship sailed to New York, via South America. Many other trips followed.

The photo and the text were adapted from the book by G.A.Tokaty, entitled "A History and Philosophy of Fluid Mechanics," Dover Publications, Inc. (1994) (originally published by G.T. Foulis & Co., Henley-on-Thames, 1971).