Aimo Lahti with a Suomi KP/31.

Aimo Lahti was born 118 years ago today in Viiala, Finland. He was the greatest gun designer in Finnish history, which makes him a big frog in a pretty small pond. But he was influential far beyond the borders of his Scandinavian homeland.

As a Finnish biography by Simo Kärävä says:

Asesuunnittelija Aimo Johannes Lahti (28.4.1896 Akaan Viiala – 19.4.1970 Jyväskylä), jonka suunnittelemat aseet tulivat 1930-luvun sotilaille ja suojeluskuntalaisille sekä sotiemme veteraaneille tutuiksi usein toistuneen koura- ja olkatuntuman kautta, on jäänyt ihmeteltävän vähälle huomiolle sotia ja puolustusvoimia käsittelevässä kirjallisuudessa sekä tämän vuoksi myös melko tuntemattomaksi muille suomalaisille, sotilaita ja aseharrastajia lukuun ottamatta.

via Aimo Lahti.

Lahti-designed 20mm AA gun VKT 40.

Yeah, that. There’s really no run-on sentence like a run-on sentence in Finnish. Anyway, Aimo is little known in the Anglosphere, but his name rings a bell because two of his best-known guns bore his own name: the Lahti M/35 automatic pistol (also adopted in Denmark and in Sweden as the M/40) which combined the natural-pointing grip angle of the Luger with a completely different mechanism, and the Lahti M/39 semiautomatic antitank rifle, advertised for years in the pages of American Rifleman and other 1960s gun magazines. The M/39 was the object of every boy’s envy, later, even if by 1939 it was already marginal medicine on tanks. Lahti would use the same basic mechanism in the beefier VKT 40 anti-aircraft gun, usually seen as a twin mount.

He also co-designed the standard Finnish light machine gun of the Winter and Continuation Wars, the Lahti-Saloranta L/S 26. (It would be replaced by Russian DP LMGs which were captured in vast quantities). He was also responsible for some of the Finnish improvements to the Mosin-Nagant rifle, and for a modified Maxim for aerial and AA use called the VKT. All in all he designed over 50 weapons, counting designs like the M/27 rifle (a modified Mosin).

Lahti’s most influential gun did not bear his name at all. It was the Machine Pistol (“Konepistooli” or KP) 31, the famous “Suomi” (a word which just means “Finland.”) While by 1931 this submachine gun was not entirely revolutionary, we need to bear in mind that the 1931 model was an update of a 1926 model, which in turn was an update of a 1922 run of prototypes. That makes the Suomi, for all intents and purposes, a contemporary of the early Thompson, yielding primacy only to the Thompson and the German MP18.

Like those guns, the Suomi featured sturdy, machined parts and a wooden stock and was very heavy, especially with a loaded drum magazine. The first Suomi drum was unreliable; it was replaced, while a new drum was being designed, by the four-column “casket” mag, that squeezed the four columns down to a single feeding position. The casket mag was a Suomi original that has echoes today in some Russian designs and the Surefire 60- and 100-round magazines.

Suomi 50-round Casket mag. From ARFCOM.

The Russian submachine guns of the mid-20th Century all owed a great deal to the Suomi design. The PPSh drum is a rather direct copy of the second, reliable Suomi design and shares its 71-round capacity. The Soviet designers were never slow to adapt a foreign idea that could be turned to Soviet military purposes.

Sweden, which built Suomis under license, used the Suomi mags as the feed system for their indigenous submachine gun, the M45 Carl Gustav (and M45 “Swedish K” mags work in a Suomi). But that’s another post.

After the Continuation War ended in 1944, Finland was occupied by a Soviet-dominated Allied Control Commission (there were a couple of token Brits) and by Finnish communist quislings who had been indoctrinated for years in the USSR and were determined to bring the joys of the Russian Revolution to Finland. However, the Finns had hidden tens of thousands of arms, and the thought of the whole nation rising in guerrilla warfare terrified the Soviets a little and their puppets a lot. The Finnish communists reinvented themselves as a political party, competing at the ballet box, and their secret police withered away when their Soviet puppetmasters withdrew.

The spiteful Soviets, whose troops had been shot full of holes by many Lahti designs, demanded that that the Finn retire from arms design, and he did, living on a pension until 1970. His only child became a Finnish Air Force aviator and perished during the Continuation War.

There is a biography of Lahti, Aimo Lahti: Finnish Weapons Designer by Maire Vaajakallio, but it is, alas, only available in the Finnish language.