British submarine flotilla in the Baltic

A British submarine flotilla operated in the Baltic Sea for three years during the First World War.^[1] The squadron of nine submarines was attached to the Russian Baltic Fleet. The main task of the flotilla was to prevent the import of iron ore from Sweden to Imperial Germany. The success of the flotilla also forced the German Navy in the Baltic to keep to their bases and denied the German High Seas Fleet a training ground. The flotilla was based in Reval (Tallinn), and for most of its career commanded by Captain Francis Cromie.^[2]

The flotilla originally consisted of six E-class and five C-class submarines. The smaller C-class submarines reached the Baltic Sea from the White Sea^[3][4] via northern rivers;^[5] the long-range E-class submarines managed to enter the German backwaters by passing undetected through the narrow and shallow Danish Straits. Two submarines were lost to stranding and one went missing, now presumed sunk by a mine.

In 1918, the German occupation of Tallinn and the Brest-Litovsk peace treaty forced the flotilla to move to Helsinki, under the protection of the Finnish Socialist Workers' Republic. The German intervention in the Finnish Civil War and the landing of the 10,000-strong German Baltic Sea Division in Hanko forced the crew to scuttle the eight remaining submarines and the three support ships, Cicero, Emilie and Obsidian, outside Helsinki harbour.

A similar fate awaited the flotilla's Russian counterpart. The Ice Cruise of the Baltic Fleet had left four Russian Holland type submarines without support in Hanko. The arrival of German troops under Rüdiger von der Goltz on 3 April forced the Russians to hastily scuttle the submarines—including AG 12 and AG 16—in Hanko harbour.