This submachine gun was reportedly developed at Rheinmetall (whose
armaments division was branded as Dreyse) at the end of World War I,
although the associated patent is actually dated to October 1919. In any
case, it was one of the earliest German SMG designs after those of
Bergmann, Schwarzlose, and Walther. The Rheinmetall submachine gun
utilized an interesting layout in which the return spring was situated
inside the stock at a canted angle, and was connected by a rod to the rear
of the bolt. Housing the return spring in the buttstock freed up space
inside the receiver and allowed it to be reduced in length, as is evident
from the initial patent sketches. The designer responsible for this system
was the young Louis Stange, who would later become better known for
designing the FG-42 machine gun in World War II.
The Rheinmetall MP20, operating on the
same principle as the Dreyse design.
By 1920, a prototype of the Rheinmetall submachine gun had been
constructed, known as the MP20. It outwardly resembled the Bergmann
M.P.18,I a great deal, with a jacketed barrel and a horizontally-feeding
box magazine, but inwardly the return spring ran inside the stock as
described. However, for some reason Stange did not take advantage of this
to reduce the receiver length, and the MP20 was ultimately similar in
dimensions to the M.P.18,I with a long tubular receiver; this may have
been deliberately done to lengthen the bolt travel and thus reduce the
fire rate. Development of the MP20 at Rheinmetall was brought to a sudden
halt upon the enforcement of the Treaty of Versailles, which forbade the
manufacture of most automatic weapons in Germany. Therefore Rheinmetall
would outsource future development of this design to their subsidiary
Solothurn in Switzerland, where it would eventually evolve into the highly
renowned Steyr-Solothurn S1-100 submachine gun by 1929.
