Designed by Piotr Wilniewczyca and Jan Skrzypinski starting in 1936, the Mors was Poland’s first domestic SMG. Polish police forces had purchased Thompsons and Suomi in the 1920s and 1930s, but the military still had no such guns by the 1930s. One of the main inspirations for the More was the Erma EMP, which was purchased in large quantity by Poland to supply to the Republican forces in the Spanish Civil War.
At any rate, the gun was developed by the State Rifle Factory in Warsaw and ready for testing in 1938. The first iteration was really disliked, with problems from accuracy to rate of fire to handling. The design would undergo several major iterations until a version was finally approved for testing in early 1939. A batch of 36 was made for those trials, plus the three prototypes made initially, giving a total production of just 39 of the guns. The German invasion in September 1939 ended the trials program, and no further examples were made.
For more details on the Mors, I suggest the article I published previously pin the subject written by Polish small arms expert Leszek Erenfeicht:
Many thanks to the Polish Army Museum for giving me access to film this exceptionally rare item for you!