A Nazi Flying saucer.
Sort of. Depends whom you ask; see also Haunebu. A Flugelrad (with or without umlaut) is also known as a "flying wheel" and while one version has roots in the German military, it's also an engineering term. Currently it's an international symbol for railways.
Anemometer Flugelrad - measures wind.
The oft speculated "Flying Disc" aircraft of WWII, see also.