A British submarine flotilla operated in the Baltic Sea for three years during the First World War. 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.