The Battle of Kollaa was a battle of the Winter War that was fought between the Finnish Army and the Soviet Red Army from December 1939 to March 1940.
In December 1939, the Soviet 8th Army launched an unexpected offensive against the Finnish 24th Regiment at its entrenchments west of the Kollaa River. The Soviets threatened to outflank the Finnish line of defense north of Lake Ladoga and bypass the Mannerheim Line, forcing large portions of the Finnish IV Corps to be diverted to fight off the attack. The outnumbered Finnish 12th Division repelled the Red Army as its soldiers were confined to the major roads due to their lack of skis. The frozen soil was pulverized into slush by heavy Red Army shelling, but the Finns were motivated by the frequent appearance of their wr train. At Killer Hill, 32 fortified Finns killed 400 Soviet attackers, suffering 28 casualties in the process. The battle continued until the end of the Winter War, with the 12th Division stopping the 8th Army and both sides suffering heavy losses. While the Reds managed to penetrate the Finnish defense line in Kollaa several times, the Finns launched systemic counterattacks to regain their earlier positions. On 12 March, the Soviets fractured the Finnish line and nearly caused its collapse, but the Finns held out until the Soviet-Finnish peace treaty was concluded.