The Lahti L-39 was an indigenous Finnish 20mm anti-tank rifle design used during the "Winter War" of World War 2. The system was designed in 1939 and produced in some 1,900 examples by the end of her run, expanding to include the fully-automatic L-39/44 anti-aircraft variant. For a time, the weapon proved effective in combating Soviet armor head-on but as armor protection on new Soviet tanks soon increased, the Lahti L-39 was relegated to other - though still useful - battlefield roles as necessary.
Two schools of anti-tank thought had ultimately developed in Finland. On one side there were those believing in the effectiveness of the smaller 13mm cartridge tied to a fast-firing machine gun-type action, providing better penetration value via higher muzzle-velocity. On the other side there stood those believing in a larger-caliber 20mm rifle. Though slower-firing, the 20mm shell inherently held sufficient benefits in being able to penetrate the then known armor thicknesses of enemy tanks. Finnish patriot Aimo Johannes Lahti (1896-1970), the self-educated weapons designer, attempted to settle the debate - he himself favoring the larger 20mm projectile weapon. Lahti set forth to design both a 13.2mm anti-tank machine gun and a 20mm anti-tank rifle. Evaluation would soon enough reveal the 20mm cartridge to be the way of things.
By the time of the Winter War - the Soviet invasion of Finland - anti-tank weaponry for the Finns was in desperately short supply with only a few 20mm and some 13.2mm weapons in circulation. The 13.2mm breed was quickly found to be useless against even the base Soviet armor. Though these 13.2mm systems offered up their high rate-of-fire, the projectiles did little in the way of penetrating armor. Those 20mm systems that were in use, however, delivered much better results. As such, a priority on 20mm anti-tank weapons was put in motion and Amios Lahti ultimately produced his memorable L-39.
The L-39 maintained a most unique external appearance. The operator was braced by a curved padded shoulder piece. The pistol grip and trigger group were set aft of the receiver. The massive curved box magazine was fitted to the top of the receiver. To the forward portion of the weapon was supported by a decidedly Finnish bipod sporting ski-type implements - suitable for winter weather conflict. The barrel extruded out at length and sported noticeable cooling vents akin to a pepper shaker. The 20mm cartridge of choice became the 20x138mm "Solothum Long" to be fired from a 10-round detachable box magazine. Muzzle velocity was listed at 2,600 feet per second and the firing action was semi-automatic. The weapon weighed in at an astonishing 109lbs with an overall length of 88 inches, 51.2 inches of this made up by the barrel. The L-39 carried the appropriate nickname of "Norsupyssy" (meaning "Elephant Gun").
In practice, the Lahti L-39 proved quite effective at the outset. Perhaps moreso adding to its legacy was the fact that the L-39 was equally adept at engaging just about any type of Soviet target under the Finland sun - be they armored or unarmored. The L-39 was used against bunker emplacements, low-flying enemy aircraft and enemy troops including other enemy sniper teams. A fully-automatic variant - the L-39/44 - was introduced in 1944 in limited quantity to serve as a dedicated anti-aircraft weapon system - seeing service even after World War 2. At any rate, the long-range hitting power and penetration values were a godsend for the defense of the Finnish frontier.
L-39 gun teams also took to targeting certain vulnerable parts of tanks if their cartridge was not able to penetrate the armor directly. This proved the case with the arrival of the heavier T-34 and KV-1 tanks to come. Thick armor proved the Soviet modus operandi until the end of the war and such armor essentially dwindled the L-39's reach to an extent. Additionally, the large weapon system was cumbersome to deploy and relocate with any sense of efficiency and were often left to the enemy when positions were overrun.
Though never receiving much in the way of support from the Allies, the outnumbered Finns (3-to-1) utilized what they had - a special combination of weapons and winter tactics - against the ill-trained Soviet soldier. The result became several notable early victories against the mighty Red Army, sometimes resulting in the decimation of entire army groups and the capturing of Soviet armor, weapons and ammunition. Though Finland eventually capitulated on March 12th, 1940, with the signing of the Moscow Peace Treaty the damage was ultimately done - some 126,875 Soviet personnel were killed or went missing while a further 264,908 were wounded. In contrast, the Finns suffered 25,904 dead or missing and a further 43,557 wounded. Finland lost out on 11% of its pre-war territory and over a quarter of her economic power. Her resistance, however, kept the Soviet Union from claiming complete control over all of Finland - delivering an international black eye to the Communist powerhouse. In the "Continuation War" still to come, Finland would once again take up arms against the Soviet Union - this time with material support from Germany and Italy at a time when Germany and the Soviet Union were now fully at war with one another.