Day 101 December 10, 1939

Finland. Despite primitive construction, the Mannerheim Line is remarkably effective. Cleared paths in the forest funnel Soviet troops into minefields and fields of fire pre-ranged for both machine guns and the limited Finnish artillery. Adjacent pill boxes provide mutually-supporting fire. Granite blocks and other obstacles block the killing fields to prevent tanks advancing on the Line. 7th Army on the Soviet left flank is also shelled by coastal batteries on the island of Saarenpää. Soviet battleship Oktjabrskaja Revolutsija shells Saarenpää but misses the batteries in dense fog. The Finnish batteries on the islands in the Gulf of Finland prevent the Soviet Baltic Fleet from landing troops behind the Mannerheim Line.

Baltic Fleet submarines sink three ships including two German vessels; SS Reinbeck in the Gulf of Finland (off Helsinki) and SS Bolheim in the Gulf of Bothnia. Most ships attacked by Soviet submarines are German although USSR and Germany are allies.