The Soviet-Finnish War began on November 30th, 1939. The cause of the conflict was a territorial disagreement between the USSR and Finland, which could not be solved by diplomatic means.
The first stage of fighting proceeded poorly for the Red Army, mostly due to serious underestimation of the Finnish army's fighting ability, and due to the harsh terrain on which the Red Army had to fight. Many mistakes were made during planning, cooperation, and supply of advancing units.
On December 21st, the Soviet advance on Karelia completely halted. The Red Army fortified for a defense, collecting forces for a new offensive. During the relative quiet on the front, the Red Army analyzed its mistakes, reformed its units, and developed combat plans.
In December of 1939, during a breakthrough of the Hottinen fortified region, the famous KV-1 heavy tank saw its first combat trials.
The Red Army's offensive resumed on February 1st, 1940, with the forces of the recently created North-Western Front, commanded by S.K. Timoshenko. Infantry and tanks were supported by large amounts of artillery. Up to 12000 shells were launched towards Finnish positions daily.
The Red Army's general offensive began on the morning of February 11th, 1940, after a three hour artillery barrage. In three days, the Mannerheim line was penetrated, and tanks flowed into the breech. On February 17-23rd, the Finnish forces retreated to secondary defensive lines to preserve the front. Towards the end of February, the Red Army reached the rear of the Finnish positions, around Wyborg.
On March 13th, a peace treaty was signed between the USSR and Finland. This is the day that is considered the end of the Soviet-Finnish war in 1939-1940.
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