The Suomi KP/-31 ('Suomi-konepistooli', or "Finland Machine-pistol") is a Finnish-designed submachine gun used by the forces of Finland primarily during the Second World War. The Suomi KP/-31 is regarded by many as as one of the most successful submachine gun designs of World War II. The effective use of the Suomi KP/-31 by the Finnish military against the Red Army during the Winter War would lead Soviet designers to begin designing their own submachine guns.