'Mitte' (i) was part of the German attack to take the island of Hiuumaa (Dagö in German), in the mouth of the Gulf of Riga off the coast of Estonia, within 'Siegfried' (i) (12/21 October 1941).
By this time there had been considerable naval activity on the waters round the island. The Soviet destroyer Gnevnyi sank on 23 June after hitting a German mine. The German S-boote S-43 and S-106 were lost to Soviet mines on 27 June. To the north of Hiiumaa, on 1 July, the Soviet submarine M-81 succumbed to a German mine. In the waters of Hiiumaa itself, on 25 June the Soviet minesweeper T-208 hit a German mine and was destroyed. The same fate befell the Soviet minesweepers T-216 on 7 July and T-201 on 30 July. On 10 August the Soviet submarine Shch-307 fired a torpedo at the German U-144, which was hit and sank.