From: https://en.wikipedia.org/wiki/BMW_R75
The BMW R75 is a World War II-era motorcycle and sidecar combination produced by the German company BMW.
In the 1930s BMW were producing a number of popular and highly effective motorcycles. In 1938 development of the R75 started in response to a request from the German Army.
Preproduction models of the R75 were powered by a 750 cc side valve engine, which was based on the R71 engine. However it was quickly found necessary to design an all-new OHV 750 cc engine for the R75 unit. This OHV engine later proved to be the basis for subsequent post-war twin BMW engines like the R51/3, R67 and R68.
