During “The Winter War” of 1939-40, the Soviets sent a massive number of troops into tiny Finland. In the process they killed around 25,000 Finnish troops, yet the badly outnumbered Finns killed more than 125,000 Soviet troops and wounded more than 250,000. Various factors must be considered in the Finnish successes. They were fighting for their country on their home ground—with nowhere to retreat. Because it was their home ground, the Finns—many of whom were hunters and woodsmen—used every tree and hill to their advantage. Virtually every Finnish soldier fighting in The Winter War was an accomplished skier, giving that soldier great mobility over the frozen, snow-covered terrain. Another important factor was the fact that many Finnish troops were either professional hunters or farmers who hunted for the pot and were used to making each shot count. Finnish hunters also made good snipers, the most famous of which was Simo Hayha, who had 505 confirmed kills of Soviet troops, substantially more if unconfirmed kills were counted.
Finnish troops had another advantage as well in their Suomi KP/31 Submachinegun. Note that Suomi actually means Finnish, while the KP stands for “konepistooli,” which is Finnish for submachinegun. The KP/31 was designed by armorer Aimo Lahti, with input from a Lt. Koskinen. Lahti was Finland’s best-known firearms designer, who had also designed the Lahti pistol that bore his name. Lahti’s designs were famed for their durability and their ability to function in the extreme cold of a Finland winter. Among the innovations of the KP/31 was decision to mount the spring inside the bolt, which allowed the overall length of the SMG to be kept shorter. The 50-round quad-column “coffin magazine” was another innovation that allowed a lot of rounds to be loaded into a stick magazine, which was easier to carry than a drum magazine. But, the KP/31 had a well-designed 71-round drum magazine as well. In fact, the KP/31’s drum was so well designed that the Soviets copied it for their PPSh-41.
Production of the KP/31 began in 1931, hence the designation, and by the beginning of The Winter War approximately 4,000 had been produced. Tactically, the Finns initially used the KP/31 as a light machinegun, but despite the 50-round and 71-round magazines it did not have the sustained fire capability of a true light machinegun. The Finns did make a bipod for the KP/31, which would have made it more effective in the squad automatic role. Also, light machineguns are normally chambered for a rifle round to give them greater range and striking power. Eventually, the Finns captured so many Russian Degtyaryov (DP) machineguns that they used those instead of the KP/31.