Context : The Suomi KP/-31 (Suomi-konepistooli or ``Submachine-gun Finland'') was a submachine gun (SMG) of Finnish design used during World War II. It was a descendant of the M-22 prototype and the KP/-26 production model, which was revealed to the public in 1925. 
Subject : Suomi KP/-31 
Relation : service entry
What was the year that Suomi KP/-31 entered service?