Suomi KP/-31
Oy Tikkakoski Ab · Submachine Gun · Discontinued · 1931
Also known as: Suomi-konepistooli M/31, KP/-31, KP M/31, Suomi M/31, Konepistooli
Overview
The Suomi KP/-31 is a Finnish-designed submachine gun chambered in 9x19mm Parabellum, designed by Aimo Lahti and manufactured by Oy Tikkakoski Ab from 1931. Featuring a machined steel receiver, quick-change barrel, and an iconic 70-round drum magazine, the Suomi is widely regarded as one of the finest submachine guns of the Second World War and the benchmark that other WWII-era designs attempted to match. Its heavily built, milled receiver and lengthy 314mm barrel give it exceptional accuracy and recoil control for a pistol-caliber automatic weapon, while the drum magazine delivers unmatched sustained firepower at the squad level. Operating from an open bolt with a simple blowback action, the KP/-31 achieves a cyclic rate of roughly 900 rounds per minute and a practical effective range of 200 meters. The weapon earned legendary status in the snowy forests of the Winter War, where small Finnish ski units employed it to devastating effect against numerically superior Soviet forces, directly inspiring the Red Army's own PPD-40 and PPSh-41 drum-magazine submachine guns. Though heavy at over seven kilograms loaded, the Suomi's robust construction, accuracy, and reliability kept it in Finnish service well into the 1980s and saw it licensed, copied, and exported across Scandinavia, Switzerland, and the Balkans. As the definitive example of interwar submachine gun engineering, the KP/-31 established design patterns - quick-change barrels, high-capacity drums, and milled receivers - that would shape an entire generation of pistol-caliber automatic weapons.
Specifications
| Weight (empty) | 4600 g (162.3 oz) |
| Weight (loaded) | 7040 g (248.3 oz) |
| Overall Length | 870 mm (34.25") |
| Barrel Length | 314 mm (12.36") |
| Height | 255 mm (10.04") |
| Width | 55 mm (2.17") |
| Action Type | Blowback |
| Firing Mechanism | Open Bolt |
| Trigger Type | Single Stage |
| Magazine Capacity | 70 rounds |
| Magazine Type | Drum |
| Muzzle Velocity | 396 m/s (1299 fps) |
| Muzzle Energy | 584 J (431 ft·lbf) |
| Effective Range | 200 m (219 yd) |
| Maximum Range | 500 m (547 yd) |
| Rate of Fire | 900 rpm |
| Barrel Rifling | Right Hand |
| Rifling Twist | 250 mm (9.84") |
| Number of Grooves | 6 |
| Frame Material | Steel |
| Barrel Material | Steel |
| Stock Material | Wood |
| Finish | Blued |
Calibers
- 9x19mm Parabellum · primary · 9mm NATO — also known as 9mm Luger, 9mm NATO, 9x19mm
Features
- Firing modes: Semi Automatic, Full Automatic
- Feed systems: Drum Magazine, Detachable Box Magazine, Quad Column Box Magazine
- Safety mechanisms: Trigger Guard Safety Lever, Bolt Handle Safety Notch
- Features: Quick Change Barrel, Open Bolt Firing, Machined Receiver, Select Fire, High Capacity Drum, Milled Construction, Muzzle Brake Compensator
Variants
- Suomi KP/-31 SJR — Suppressor Bracket
- Suomi KP/-44 — Simplified Wartime
- Suomi M/31 (Tank) — Vehicle Mounted
- Husqvarna M/37-39 — Swedish License
- Madsen M/44 — Danish License
- Hispano-Suiza MP 43/44 — Swiss License
Service history
Operators
- Finnish Defence Forces · adopted 1931 · as KP/-31
- Royal Danish Army · adopted 1944 · as Madsen M/44
- Swedish Armed Forces · adopted 1937 · as Kulsprutepistol m/37
- Bulgarian Army · adopted 1940 · as Suomi
- Swiss Armed Forces · adopted 1943 · as MP 43/44
- Estonian Defence Forces · adopted 1937
- Polish Armed Forces
- Croatian Home Guard · adopted 1941
Conflicts
- Chaco War (1932-1935)
- Spanish Civil War (1936-1939)
- Winter War (1939-1940)
- Continuation War (1941-1944)
- Lapland War (1944-1945)
- World War II (1939-1945)
Production
Estimated total produced: 80,000 · Production years: 1931-1944
Approximately 80,000 produced in Finland by Tikkakoski. Additional licensed production in Sweden (Husqvarna), Denmark (Madsen), and Switzerland (Hispano-Suiza) added tens of thousands more to total worldwide production.
Origin
Country of origin: Finland
Designer: Aimo Lahti
Discontinued: 1953
Notes
Production totaled approximately 80,000 units in Finland across all variants between 1931 and 1944, with additional licensed production in Sweden (Husqvarna M/37-39), Denmark (Madsen M/44), and Switzerland (Hispano-Suiza MP 43/44). The SJR variant incorporated a muzzle bracket designed to accept a suppressor sleeve. The KP/-44 was a simplified wartime version influenced by Soviet PPS-43 construction methods. The distinctive 70-round drum magazine was the direct ancestor of the 71-round drums used on the Soviet PPD-40 and PPSh-41. The KP/-31 also accepted 20-round and 50-round box magazines, as well as a less common 40-round quad-column 'casket' box magazine. Loaded weight with 70-round drum is approximately 7.04 kg; with 50-round box approximately 5.65 kg. Finnish stocks remained in reserve service until the 1980s.
Background
Finnish ski troops armed with the Suomi KP/-31 inflicted such catastrophic losses on Red Army columns during the Winter War that Soviet tacticians demanded their own industry copy the concept - the drum magazines of the PPD-40 and PPSh-41 are direct descendants of the Suomi's 70-round pattern. Designer Aimo Lahti reportedly considered the submachine gun an inferior weapon to a proper rifle, and was later embarrassed that his KP/-31 became Finland's most celebrated small arm. The Vatican even purchased a small batch for the Swiss Guard.