Naval warfare in the Winter War

The Winter War between Finland and the Soviet Union, from 30 November 1939 to 13 March 1940, included a small amount of naval warfare.

The Baltic Sea began to freeze over by the end of December, which made the movement of warships very difficult; by mid-winter, only ice-breakers and submarines could still move.

The Baltic Fleet was a provincial coastal defence force which did not have the training, logistical structure, or landing craft to undertake large-scale operations.

[2] The Finnish Navy was a coast defense force with two coastal defence ships, five submarines, four gunboats, seven motor torpedo boats, one minelayer and six minesweepers.

[1] Beside the coastal defense, the Finnish Navy also protected Åland islands and merchant vessels in the Baltic sea — only a minor part of the fleet could engage in offensive military action.

[2] In addition to its navy, Finland had coastal artillery batteries defending important harbours and naval bases along its coast.

In addition to the support of the land troops, Soviet naval forces made repeated attacks against the forts during December 1939.

During the Winter War, the Soviet submarines sank a total of five merchant ships: one Estonian (Kassari), two German (Reinbeck and Bolheim), one Swedish (Fenris), and one Finnish (Wilpas).

One Finnish auxiliary anti-submarine ship, Aura II, sank on 13 January 1940, while escorting a convoy in the Sea of Åland, near Märket Island, in action against the Soviet submarine ShCh-324.