Entering service in 1931, the 9x19mm Suomi KP/-31 submachine gun saw extensive combat with Finnish troops during their fight against Soviet forces in 1939–44. It was also manufactured under licence in Switzerland, Denmark and Sweden, and remained in Finnish service until the 1980s, an indication of its durability.

Rugged and accurate, the Suomi was a favourite with Finnish ski troops who would strike from ambush, cutting down Soviet troops, then skiing away into the woods. Initially used by the Finns as a light machine gun at infantry squad level, it eventually became a dedicated submachine gun, and since it had been designed to be more accurate than the typical SMG, it was often even used as a sniping weapon, or to supplement longer-ranged rifles such as the Mosin-Nagant. Featuring first-hand accounts and specially commissioned colour artwork, this is the story of one of World War II's most distinctive and respected infantry weapons.