The German Zundapp K800 was made from 1933 to 1938, powered by a flat four turning out up to 26 hp, running through a four speed transmission and shaft drive.  Almost 19,000 of a similar model, the KS 750, were provided to the German Wehrmacht for use in the war.  Not sure which model this is.  In the early 30s, Zundapp worked with Ferdinand Porsche on the early designs for the Volkswagen Beetle. See link at right for Revival Cycles.