12 December 1939 - DAY 13 of Winter War
Central Isthmus: Soviet troops launch reconnaissance probes at Summa in the central section of the Isthmus.
Ladoga Karelia: Group Talvela's Detachment Pajari begins its successful offensive at Tolvajärvi.
Ladoga Karelia: troops of IV Army Corps launch an offensive on the Lemetti road.
Ilomantsi: Detachment A's advance from Oinaansalmi to take Möhkö 4 km to the east grinds to a halt due to command problems.
Suursaari: the Finnish motor torpedo boats Raju and Isku lay the first offensive mine fields in front of Suursaari harbour.
The League of Nations calls on the warring parties to cease hostilities and open peace negotiations.
Finland wins authorization to buy 43 Brewster fighter aircraft from the USA.
Daily losses: 310
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13 December 1939 - DAY 14 of Winter War
Central Isthmus: Soviet troops continue their attacks with the support of artillery and tanks in the Summa-Muolaanjärvi sector. The last Finnish forward combat posts in the Perkjärvi sector are pulled back. The attacks are repulsed in all sectors of the front.
Ilomantsi: Detachment A's attack fails.
Northern Finland: Major-General K.M. Wallenius takes command of the Lapland Group.
Helsinki: Hietaniemi cemetery receives it first five fallen heroes.
Helsinki: a private umbrella organization, the Finnish Centre for Nordic Aid, is set up to organize the evacuation of Finnish children to Sweden. The first shipment of children arrives by sea in Stockholm.
Abroad: the Soviet Ambassador in Rome returns to Moscow, apparently in protest over a demonstration in support of Finland.
Washington: the US Government refuses to grant Finland a credit to purchase military materials and equipment.
Daily losses: 157
Men of 1/Er.P.8 at Ruokojärvi.