Suomi M31: Finland’s Famous Submachine Gun


Designed by Finland’s most notable arms inventor, Aimo Lahti, the m/31 Suomi submachine gun is an iconic weapon of the Winter War and the Continuation War. It is a first-generation submachine gun with a heavy milled receiver and very well-fitted parts – enough so that a series of vent holes were put in the end of the receiver tube to prevent air compression during the firing cycle. The gun is overall quite heavy (4.7kg / 10.4lb) and has a high rate of fire (~900 rounds/minute). It originally used 50-round quad-stack magazines and 71-round drum magazines, which allowed a shooter to exploit the high rate of fire without constantly having to change magazines.

The quad-stack magazines were eventually found to be insufficiently reliable, and were retired. The drum proved to be quite good in use, although quite awkward and bulky to carry (not that Finnish troops had no specialized pouches for these drums). The drum design would be taken by the Russians (handed over by a defecting Finnish officer, apparently) and copied for use in the Soviet PPD and PPSh submachine guns. In the 1950s, a simple double-stack 36 round magazine was developed and became most popular.

We also have a live firing assessment of the m/31 Suomi on InRangeTV:


  1. Unfortunately going entirely by memory (forgive me for errors in the details) but there was an interesting book, later to become a film starring the Suomi. “The Laughing Policeman'” it was and included a extension of the scene where the Bad guy, occupying the furthest back-seat of a bus, meticulously assembles his Soumi, theatrically klatching together the components before hosing the bus occupants.
    The film was pretty good, the book was better but in any case the only starring role I can recall for the Suomi.

    • And as the same source also says, the original magazines of the M31 Suomi were a 20-round box (nominal capacity 25, but never loaded to more than 20 rounds) and a 40-round drum. The 70-round drum (nominal 71) was developed after the 20-rounder was found to have an insufficient capacity and the 40-rounder simply too heavy and expensive for the capacity (not that the 70-rounder was light or inexpensive, but nevertheless it gave much better “bang for the buck”). The Swedish 50-round “coffin” for the Kpist m/37-39 (a licensed and modified Swedish copy) was then adopted as a cheaper and more compact alternative, but as Ian wrote, was found to be unreliable (partly by design, but also because it was made of too thin steel).

      The 36-round box was a licensed copy of the magazine for the Kpist m/45 “Carl Gustav”, also known as “Swedish K” SMG. First batch of them mags were bought directly from Sweden. Strangely enough, the 36-rounder was not used very commonly in conscript training, possibly because the Finnish Army wanted to save them for possible wartime use.

      • War against whom? The Soviet Union again? I thought Finland proved impossible to conquer after the Winter War (somewhat Pyrrhic victory for the Russians, since they lost so many just to gain ownership of Karelia). Did I mess up?

        • While it was not said aloud during the Cold War due to Neutrality policy and in interest of maintaining good relations, the Soviet Union was the only real military threat to Finland. Finland was not “impossible to conquer” by any means. The Winter War ended in a negotiated peace treaty primarily because Stalin feared that he might get into war with the UK and France.

          Unlike Hitler, Stalin was relatively cautious in his foreign policy. While the Soviets suffered disproportionate losses during the war, Stalin would have occupied the whole country, losses or not, if he could have been certain that there would be no military intervention by the Allies.

          • In the peace they were able to get from Stalin, the Finns gave up a LOT of their best farmland in the Karelian Peninsula. When Hitler invaded Russia, the Finns made a partial alliance and retook the lost territory.

            Finns did not participate in the rest of Barbarossa, but were fighting Russians on the northern end of things. As the Russians retook the peninsula, the Finns made another peace, and had to assist in ejecting the remaining Germans from Finland.

      • “Swedish 50-round “coffin” for the Kpist m/37-39 (a licensed and modified Swedish copy) was then adopted as a cheaper and more compact alternative, but as Ian wrote, was found to be unreliable (partly by design, but also because it was made of too thin steel).”
        I wonder how reliability of 50-round coffin magazine compared to earlier Swedish 56-round magazine for their Kpist m/37:
        which unlike SUOMI were firing 9 mm skarp patron m/07 (i.e. 9×20 mm SR Browning)

  2. In the InRange video Ian says that the Kp44 was the replacement for the M31 Suomi. It would be more accurate to say that it was the intended replacement. Only 10,000 were made, which was not even nearly enough to replace the M31. The actual replacements for the M31 Suomi in Finnish Army inventory were 100,000 Chinese Type 56-2 and another 100,000 ex-East German MPi-KM(S) 72 assault rifles bought in early 1990s. They also finally replaced the M39 Mosin-Nagants, most of which were still in inventory in 1990.

  3. This is solid gun – the kind of thing I like (no crappy, cheesy poorly welded stampings like on, you know what…), but heavy and conceivably not cheap to make. It resembles to some degree Thompson, in the way the magazine inserts; it seem to me superior to usual magazine well. When comes to person of its designer, Mr. Lahti, he is my hero (I suppose I do not have to be of his nationality to claim my affinity). Also, his son, fighter pilot paid with his life for defense of his country. As I understand, Mr. Lahti was interrogated after war by Anglo-American intelligence services. True patriot in any sense of the word.

    Again, this is an excellent show; first time I saw Suomi SGM so close with correct interpretation. Thanks!

    • Denny, just for your information Aimo Lahti was the only man in finnish military who had permission to drink during worktime, a permission granted by marshall Mannerheim.
      He was no easy person, and when in hangover he was unbearable – so give man a drink and all goes OK, apparently it went so 🙂

  4. Stalin’s behaviour during the Winter War must have been largely governed by the fact that both France and Britain considered Russia as an ally of Germany, and thus a de facto enemy. British sympathy for Finland was total in the British press during the Winter War, during what was known as the Phoney War for the UK.

    The French and British created an army to go to the aid of Finland. Proving this is way beyond my resource, but if you anything about the Norway campaign, then the fact the British even had skis would suggest they’d been planning to fight in Finland.

    After March 1940 Finland was beaten, but by that time America had started getting behind the Finns with words and bandages, and were threatening economic action. Stalin could have conquered Finland, but he was a better gambler than Hitler. The peace that ended the Winter War left Russia with Karelia (where my mother lived), which gave protection to Leningrad. It also avoided the risk of actually going to war with Britain and France; and the chance of US economic action.

    • Supposing that Stalin was insane enough not to care about economic backlash(and said “Screw the Capitalists, kill them all!!”) to fight the British and the French in 1940 with the idea that the Western Powers were unlikely to send enough men and machines to fight properly, how would things have gone? Would Hitler decide to backstab Stalin anyway? Would millions of Russians die in the attempt to defoliate everything north of Karelia and thus serve as fertilizer for the next generation of trees? Would France lose tons of soldiers trying to mount a bayonet charge against a horde of Soviet conscripts? Would the British Fleet Air Arm get its time to shine? Find out if anyone creates “Alternate History: The Frightening Forests of Finland!”

      Please don’t point a literal Flak cannon in my direction.

      • No Flugzeugabwehrkanone… Just the “best laid plans…”

        Recall that Stalin and Hitler, via their foreign ministers, Molotov and Ribbentrop had attached a secret annex to their treaty. Germany got most of Poland, and to hive Memel off of Lithuania as their “sphere of influence.” Stalin got to resurrect the old Czarist realm: takeover eastern–Formerly Russian–Poland, Latvia, Lithuania, Estonia, eventually Moldova, aka “Bessarabia” and of course, the old Grand Duchy Finland, which had been wrested from Swedish control by the Czar back in 1809.

        Recall that Britain and France were not exactly keen on reprising the 1914-18 experience in Belgium and northeastern France, and dreamed of one or another way to overtax and overheat the German economy, or deny it one or another essential resource it was deficient in. This was not entirely ill-informed. No bauxite, nickel (Finland!), tin (Bolivia!), tungsten (Spain!), chrome (USSR!), molybdenum, beryllium, platinum (USSR!), etc. But the real target was Swedish ball bearings (“Volvo” Latin for “I roll..”) and iron ore.

        So Franco-British leaders plotted air raids against Baku and the Caucasus from Middle-Eastern states, or a Romania offered sufficient inducements for basing rights as a means of attacking, *ahem* Germany’s oil supplies.
        Operation Stratford called for 100k British and French troops to attack through Norway into Central Sweden in the name of coming to the aid of Finland, of course, but with crocodile tears, and alternate objectives to deny the Baltic region and its trade to Germany. Similar planning led to Operation Wilfred and Plan R4. Stalin may have ignored mounting evidence and scolded and condemned accurate intelligence reports that Germany was preparing its June 1941 Barbarossa surprise attack… Yet, strangely, he lent all too much credence to the idea that unless terms could be reached with Finland after the Timoshenko breakthrough of the Mannerheim line, he’d have to fight the capitalist powers UK and France, and possibly one or another Scandinavian nation, like Sweden, into the bargain.

        I’m not sure that the French would have been too thrilled. If dying for Danzig seemed objectionable, imagine Hangö/Hanko. Or the Åland islands. Or whatever.

        France, Britain, Italy, even South Africa, all contributed weapons and aircraft and supplies to Finland, but much of it, like the Terni 7.35mm carbines, the Chauchat fusils-mitrailleurs, the ancient obsolete cannon without recoil systems. etc. etc. arrived too late for the Talvisota/Winter War, and instead were utilized to free up additional equipment for the Continuation War, 1941-1944.

      • “Would Hitler decide to backstab Stalin anyway”
        Considering expansionism of Soviet regime and Nazi regime clash was unavoidable (cf. Lebensraum)

      • “French”
        Even assuming French forces are ready how you would transport them to Finland?
        In 1930s default method for troop transport was by ship or by railroad. Aerial transport was technically possible but much less efficient than today.
        In 1939 Finland was adjacent to:
        1. Norway
        2. Soviet Union
        3. Gulf of Finland
        4. Gulf of Bothnia
        5. Sweden
        2 and 4 are impossible to use due to presence of RKKA and RKKF
        I doubt if 5 would allow passage, surely Swedish volunteers fight on Finnish side, but Sweden would rather want to stay neutral, rather than risking event: III Reich declare war to Sweden.
        3 is risky due to Kriegsmarine operating in Baltic sea
        1 seems best safety-wise but I do not know if Norway would allow passage?

      • The way I see it is that Stalin was a paranoid gangster, but that paranoia did not include Hitler’s obsession with his own genius. Stalin walked into Estonia, Latvia and Lithuania unopposed as part of his dirty deal with Hitler. The Finns fought, and showed up his army for what it was after he had murdered almost all it’s competent officers; and almost anyone else in Soviet Russia with half a brain.
        So during the Winter War Stalin must have realised just how much he had screwed up. My mother told stories of Soviet troops who were serving in the semi desert regions to the south, who were put on a train, marched to the front, and captured by the Finns if they were lucky (because it they’d not been captured they would have frozen to death in their desert uniforms: although those that were captured probably were shot when they were repatriated).
        After the Winter War Stalin stopped murdering his generals, at least he stopped murdering most of them.
        They Winter War convinced Hitler Soviet Russia was just needed a boot to it’s rotten door to bring the whole lot down; but it taught Stalin enough lessons to be able to survive up to December 1941, and then the Russian people won the war for him, no matter how little he deserved them.

    • The fact that they had skis proves nothing. Its harder to ski in norways montaneous landskape but still better then wading through deep snow.

  5. I’ve read that the ‘motti’ tactics weren’t really what the Finns had in mind. Cutting a long column into chunks would precipitate a chaotic retreat, or surrender, from any normal army. To the Finn’s horror, the Russians, due to fear of their own leadership, or just incompetence, would dig in and fight to the last cartridge.

    Stalin had already purged almost every officer with any experience or brains. The army that invaded Finland was ‘politically reliable’ at the expense of the most basic competence.

    • And thus the only way to get Russian soldiers to panic and flee was assassinating the commander and the commissar! Without the political officer, who would enforce the “no retreat” order?

      Random Finn: “At least when the Russians die we get all their guns and ammunition at a discount. And they kindly left us lots of tanks and planes to salvage or reuse once we cleaned out the crews’ remains. Who could refuse the offer of wonderful toys?”

  6. Adolf Hitler bought into his own hubris since he was a reckless gangster gambler, ’tis true… His initial ideas seemed to be the German 2nd Reich circa 1917-1918 when the Bolsheviks signed the Treaty of Brest-Litovsk leaving Germany in possession of Ukraine, Belarus, the Baltic States, Poland… Resurrect that stillborn empire–the “Lebensraum” in the east. When France and the UK were defeated in six weeks in “Fall Gelb” and “Fall Rot” instead of being mired in four years of attritional warfare, he concluded that with France out of the war already, that the Russians were a giant with feet of clay… Doubtless the poor performance by Stalin’s “mini-me” Kliment Voroshilov figured into the calculations that the Red Army could be destroyed in massive encirclement battles, which essentially happened. It’s just that the Soviet State did not collapse, and readied a second and third iteration of the Red Army by 1944…

    • German intelligence vastly underestimated Soviet ability to gather fresh manpower for the army. Even as late as Summer 1943 the Germans were again surprised by the armies Soviets had amassed for a counter-offensive after German Operation Citadel failed to reach its objectives. Despite heavy losses on the Soviet side they were able to start offensive operations very rapidly.

      • “Operation Citadel”
        Regarding Unternehmen Zitadelle: Soviet Union was able to get info about it via espionage for more data see:
        On other hand III Reich’s espionage attempts were hindered by fact that there 2 independent and competing (if not hostile to each other) espionage organizations: Abwehr (see: Wilhelm Canaris) and Sicherheitsdienst des Reichsführers-SS (see: Ernst Kaltenbrunner)

        • The Soviets had superb intelligence from multiple sources that the Germans were readying a surprise attack in June 1941… Stalin simply discounted it, and proclaimed anyone who hinted or intimated that the Stalin-Hitler/ Molotov-Ribbentrop pact might not hold until the Soviets had completed consolidation of the 1939-40 conquests, readying defensive lines, etc. etc. was a traitor or a stooge of Western disinformation.

          The Germans had a complete set of half-burned plans about possible offensives into Belgium seized by the Belgians and French when an officer ill-advisedly agreed to allow his buddy to fly him to a meeting during the “Sitzkrieg/ Phony war/ drôle de guerre…” It was largely discounted as supremely clever misinformation that the methodical, plodding, pedantic Germans had planted… A ruse, in other words.

          Intelligence failings were frequent and widespread, certainly.

          • “Stalin simply discounted it, and proclaimed anyone who hinted or intimated that the Stalin-Hitler/ Molotov-Ribbentrop pact might not hold until the Soviets had completed consolidation of the 1939-40 conquests, readying defensive lines, etc. etc. was a traitor or a stooge of Western disinformation.”
            In fact Soviet Navy go into battle readiness (readiness No.1) before German attack.
            Happenings in 1941 are obscured by fact of post-war propaganda.
            After Stalin’s death naive Stalin version was very handy.
            To explain why we must go to 1950s or using Soviet Union timeline – Khrushchev’s Thaw and person of First Secretary of the Communist Party of the Soviet Union (further I will simply use Secretary term for simplicity). Secretary was gambling in risky game – launched de-Stalinization which was basically 180° turn in VKP(b) policy, this clearly was seen as danger by some members of said party. However Secretary has powerful ally in person of Zhukov, already known as Marshall of Victory – whatever it was well-earned title or effect of propaganda is hoax is irrelevant here. If Secretary would order truly honest investigation about tragedy of 1941, it would clearly point to Zhukov as responsible (at least partly) for that.
            Thus it never happened.

        • After he was captured, the proudest moment claimed mentioned by Goering (sorry for no umlaut, but I do not know where they are, and I am lazy) to his Allied interrogators was when he was saved for a firing squad by a passing a Luftwaffe unit, after Hitler had killed himself..

          This may seem way off the topic of the M31, and shooting from unrelated political issues; but Finland’s (and Sweden’s) war is so far removed from what most on here, who are not from eastern and northern Europe, know about as to be worth dwelling over for the light it shines on the way both Nazi and Soviet leaders ran their war..

          This thread is also worth remembering for those interested in last ditch weapons; the PPS, and all the competing German guns of the last World War’s last year.

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  9. According a book about Aimo Lahti and his guns, the muzzle brake in Suomi SMG model 2 made Lahti furious. He had indented the sloped fore end of first model to work as a kind of muzzle brake. When the muzzle blast hit the sloped surface to prevented barrel rising while shooting full auto. No idea if it really worked that way – I have only fired short burst (and semi auto) with this gun.

  10. I happened to build one of these from a parts kit recently (and no it’s not the TNW semi auto it’s the original open bolt design) and I was just wondering, is it safe to use +P ammunition in one of these or will that harm the gun? I have to mention too, I am so glad I got one of these. It’s a pretty awesome gun and I have zero complaints about it. I know a lot of people don’t like heavier guns like this but in my opinion the hefty weight is well worth the reduction in recoil. I also shoot lefty and I’ve never been hit in the face from the brass being thrown out of the gun.

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