Suomi M-31 SMG
Encyclopedia
The 'Suomi KP/-31' was a submachine gun
(SMG) of Finnish
design that was in service 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. The Suomi-konepistooli KP/-31 is often abbreviated to Suomi KP.
The Suomi KP/-31 is regarded by many as one of the most successful submachine guns of World War II, also the soon developed 71-round drum magazine
was later copied and adopted by the Soviets
for their PPD-40
and PPSh-41
submachine guns. The accuracy compared to the mass-produced PPSh-41 was superior however, thanks in part to a noticeably longer barrel, with the same rate of fire
and the equally large magazine capacity. The major disadvantage of the Suomi-KP was its high production costs.
The Suomi KP/-31 also incorporated a few new design features, including an arrangement whereby the spring was mounted inside the bolt in order to make the gun shorter. Its 50-round quad-column "Casket" box magazine was more reliable than the early 50-round "bullets loaded nose down" drum magazine, and similar applications were used on the Argentine C-4 submachine gun
and present-day 60-round 5.45x39mm AK-74 compatible magazines.
The M-22 and KP/-26 were made by Konepistooli Oy, founded by Master Armorer Aimo Lahti
, Captain V. Korpela, Lieutenant Y. Koskinen and Lieutenant L. Boyer-Spoof. The Suomi KP/-31 was designed by Koskinen and Lahti.
The Suomi KP/-31 went into serial production in 1931 by Tikkakoski Oy and most of these weapons were bought by the Finnish Defence Forces
. The Finnish Defence Forces were equipped with about 4000 Suomi KP/-31 submachine guns when the Winter War
started. During the course of the war, the design was altered with the addition of a muzzle brake
, which increased the submachine gun's overall length by 55 mm. The revised version was designated KP/-31 SJR (suujarru, or "muzzle brake"). Aimo Lahti was displeased with this revision, believing that it reduced the weapon's reliability. Ultimately, roughly half of the KP/-31s in Finnish service were of the SJR version. Initially the KP/-31 was issued as a substitute for a light machine gun
, and proved inadequate in this role. Instead, soldiers learned by trial and error how to use submachine guns to the best effect. By the time of the Continuation War, Finnish doctrine had been altered to include both a KP/-31 and a light machine gun (usually a captured Degtyaryov DP) in every infantry squad, and by 1943 this had been expanded to two KP/-31s per squad. KP/-31 production continued with the intention of adding a third submachine gun to each squad, but this plan was shelved in 1944 when the Continuation War ended.
A specialized bunker version was also produced in very small numbers (a total of 500 built) in 1941, with a thinner barrel shroud
to allow firing through the narrow ports of defensive bunkers. This version lacked a shoulder stock and was equipped with a pistol grip
. An even rarer version was produced for use as a secondary gun in the firing ports of Vickers Alt B Type E 6-Ton
tanks, but only a few dozen were built before production was canceled due to the outbreak of the Winter War. Production never resumed, as captured Degtyaryov DP machine guns proved far superior in this role. Like the bunker version, the tank version had a pistol grip and no buttstock, and it could be quickly removed from the tank and fitted with a standard barrel shroud for infantry use if needed. The tank version remained in the Finnish Army's inventory through the 1980s, despite the tank it was designed for being retired in 1959, possibly because the Army forgot that they existed.
The Suomi KP was also manufactured under licence in Sweden
, Denmark
, and Switzerland
, where it was known as the Hispano-Suiza
MP43/44. Tank and pillbox variants were also developed and produced in Finland.
In 2009, a semi-automatic version of the Suomi KP was produced for civilian sale in the United States, replacing the receiver and lengthening barrel to meet the standards of the National Firearms Act
.
Submachine gun
A submachine gun is an automatic carbine, designed to fire pistol cartridges. It combines the automatic fire of a machine gun with the cartridge of a pistol. The submachine gun was invented during World War I , but the apex of its use was during World War II when millions of the weapon type were...
(SMG) of Finnish
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
design that was in service during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. It was a descendant of the M-22 prototype and the KP/-26 production model, which was revealed to the public in 1925. The Suomi-konepistooli KP/-31 is often abbreviated to Suomi KP.
The Suomi KP/-31 is regarded by many as one of the most successful submachine guns of World War II, also the soon developed 71-round drum magazine
Drum magazine
A drum magazine is a type of firearms magazine that is cylindrical in shape, similar to a drum. Instead of rounds being stored flat, as in a more common box magazine, rounds in a drum magazine are stored in a spiral around the center of the magazine, facing the direction of the barrel.There are...
was later copied and adopted by the Soviets
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
for their PPD-40
PPD-40
The PPD is a submachine gun originally designed in 1934. The PPD had a conventional wooden stock, fired from an open bolt, and was capable of selective fire....
and PPSh-41
PPSh-41
The PPSh-41 was a Soviet submachine gun designed by Georgi Shpagin as an inexpensive, simplified alternative to the PPD-40. Intended for use by minimally-trained conscript soldiers, the PPSh was a magazine-fed selective-fire submachine gun using an open-bolt, blowback action...
submachine guns. The accuracy compared to the mass-produced PPSh-41 was superior however, thanks in part to a noticeably longer barrel, with the same rate of fire
Rate of fire
Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. It is usually measured in rounds per minute , or per second .-Overview:...
and the equally large magazine capacity. The major disadvantage of the Suomi-KP was its high production costs.
The Suomi KP/-31 also incorporated a few new design features, including an arrangement whereby the spring was mounted inside the bolt in order to make the gun shorter. Its 50-round quad-column "Casket" box magazine was more reliable than the early 50-round "bullets loaded nose down" drum magazine, and similar applications were used on the Argentine C-4 submachine gun
Hafdasa C-4
The HAFDASA C-4 is a submachine gun of Argentine origin and is chambered in 9mm and .45 calibres. It has an aluminium lower receiver and is fed from a wide box magazine . Its magazine insert has a dust cover that folds open forward to form a grip shrouding the front of the magazines...
and present-day 60-round 5.45x39mm AK-74 compatible magazines.
The M-22 and KP/-26 were made by Konepistooli Oy, founded by Master Armorer Aimo Lahti
Aimo Lahti
Aimo Johannes Lahti was a self-taught Finnish weapons designer. Out of the 50 weapons that he designed, the best known is the Suomi M-31 SMG. Other well-known weapon designs include the Lahti-Saloranta M/26 LMG, Lahti L-35 pistol and Lahti L-39 anti-tank rifle...
, Captain V. Korpela, Lieutenant Y. Koskinen and Lieutenant L. Boyer-Spoof. The Suomi KP/-31 was designed by Koskinen and Lahti.
The Suomi KP/-31 went into serial production in 1931 by Tikkakoski Oy and most of these weapons were bought by the Finnish Defence Forces
Finnish Defence Forces
The Finnish Defence Forces are responsible for the defence of Finland. It is a cadre army of 15,000, of which 8,900 are professional soldiers , extended with conscripts and reservists such that the standard readiness strength is 34,700 people in uniform...
. The Finnish Defence Forces were equipped with about 4000 Suomi KP/-31 submachine guns when the Winter War
Winter War
The Winter War was a military conflict between the Soviet Union and Finland. It began with a Soviet offensive on 30 November 1939 – three months after the start of World War II and the Soviet invasion of Poland – and ended on 13 March 1940 with the Moscow Peace Treaty...
started. During the course of the war, the design was altered with the addition of a muzzle brake
Muzzle brake
Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm or cannon to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire...
, which increased the submachine gun's overall length by 55 mm. The revised version was designated KP/-31 SJR (suujarru, or "muzzle brake"). Aimo Lahti was displeased with this revision, believing that it reduced the weapon's reliability. Ultimately, roughly half of the KP/-31s in Finnish service were of the SJR version. Initially the KP/-31 was issued as a substitute for a light machine gun
Light machine gun
A light machine gun is a machine gun designed to be employed by an individual soldier, with or without an assistant, as an infantry support weapon. Light machine guns are often used as squad automatic weapons.-Characteristics:...
, and proved inadequate in this role. Instead, soldiers learned by trial and error how to use submachine guns to the best effect. By the time of the Continuation War, Finnish doctrine had been altered to include both a KP/-31 and a light machine gun (usually a captured Degtyaryov DP) in every infantry squad, and by 1943 this had been expanded to two KP/-31s per squad. KP/-31 production continued with the intention of adding a third submachine gun to each squad, but this plan was shelved in 1944 when the Continuation War ended.
A specialized bunker version was also produced in very small numbers (a total of 500 built) in 1941, with a thinner barrel shroud
Barrel shroud
A barrel shroud is a covering attached to the barrel of a firearm, that partially or completely encircles the barrel which prevents operators from injuring themselves on a hot barrel. Slides, extensions of the stock that do not fully encircle the barrel, and the receiver of a firearm itself are...
to allow firing through the narrow ports of defensive bunkers. This version lacked a shoulder stock and was equipped with a pistol grip
Pistol grip
On a firearm or other tool, the pistol grip is that portion of the mechanism that is held by the hand and orients the hand in a forward, vertical orientation, similar to the position one would take with a conventional pistol such as the M1911....
. An even rarer version was produced for use as a secondary gun in the firing ports of Vickers Alt B Type E 6-Ton
Vickers 6-Ton
The Vickers 6-Ton Tank or Vickers Mark E was a British light tank designed as a private project at Vickers. It was not purchased by the British Army, but was picked up by a large number of foreign armed forces and was copied almost exactly by the Soviets as the T-26. It was also the direct...
tanks, but only a few dozen were built before production was canceled due to the outbreak of the Winter War. Production never resumed, as captured Degtyaryov DP machine guns proved far superior in this role. Like the bunker version, the tank version had a pistol grip and no buttstock, and it could be quickly removed from the tank and fitted with a standard barrel shroud for infantry use if needed. The tank version remained in the Finnish Army's inventory through the 1980s, despite the tank it was designed for being retired in 1959, possibly because the Army forgot that they existed.
The Suomi KP was also manufactured under licence in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, and Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, where it was known as the Hispano-Suiza
Hispano-Suiza
Hispano-Suiza was a Spanish automotive and engineering firm, best known for its luxury cars and aviation engines in the pre-World War II period of the twentieth century. In 1923, its French subsidiary became a semi-autonomous partnership with the parent company and is now part of the French SAFRAN...
MP43/44. Tank and pillbox variants were also developed and produced in Finland.
In 2009, a semi-automatic version of the Suomi KP was produced for civilian sale in the United States, replacing the receiver and lengthening barrel to meet the standards of the National Firearms Act
National Firearms Act
The National Firearms Act , 73rd Congress, Sess. 2, ch. 757, , enacted on June 26, 1934, currently codified as amended as , is an Act of Congress that, in general, imposes a statutory excise tax on the manufacture and transfer of certain firearms and mandates the registration of those firearms. The...
.
Users
- 5505 were bought from 1940-1942.: 1250 were bought from 1942-43.: Madsen and Hovea made at least 1,400 M/31 copies designated M/41 derived from the Lettet-Forsøgs submachine gunLettet-Forsøgs submachine gunThe Lettet-Forsøgs was a variant of the Suomi KP/-31 submachine gun of Finnish origin adapted for Danish service. It was made from stainless steel with a tubular buttstock and a distinctive ball-shaped wooden foregrip intended to improve ergomomic flexibility for the user when handling the weapon...
.: 485 purchased in 1937.: 3,042 were ordered by Germany from Finland during The Second World War and likely issued to the WehrmachtWehrmachtThe Wehrmacht – from , to defend and , the might/power) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the Heer , the Kriegsmarine and the Luftwaffe .-Origin and use of the term:...
and SS. Also 120 Suomis were presented to the German troops of AOK Norwegen in 1942 for use on the Finnish Front. Most of these weapons left Finland with German troops in 1944 and were subsequently used in other theaters of the war.: Norwegian police troops trained in SwedenNorwegian police troops in Sweden during World War IIThe Norwegian police troops in Sweden during World War II consisted of around 13,000 troops, recruited from Norwegian refugees and trained at a number of secret camps in Sweden.-Background:...
used the Swedish m/37-39 variant. Used by the Norwegian armed forces after the war until the 1980's, primarily by the Navy and the Home Guard.: Used by Polish Police (PolicjaPolicjaPolicja is the generic name for the police in Poland. The Polish police force was known as policja throughout the Second Polish Republic , and in modern post-communist Republic of Poland since 1990. Its current size is 103.309 officers and ca. 12.000 civilian employees...
): 35.000 made under license by Husqvarna Vapenfabriks AB just before and during WWII, some were also imported from Finland. Designated kpist m/37 (9mm Browning Long9mm Browning LongThe 9 mm Browning Long is a military centerfire pistol cartridge developed in 1908 for the 9 mm Browning pistol adopted by Belgium, France, the Netherlands, and Sweden...
caliber) after the year of adaption, in 1939 Sweden decided to switch to 9 mm Parabellum and the new weapons were designated kpist m/37-39. : Used captured weapons.