This was a German pair of plans ('Beowulf I' and 'Beowulf II') to occupy the islands of Saaremaa, Hiiumaa and Muhu (Ösel, Dagö and Moon in German) off the east coast of Estonia in the mouth of the Gulf of Riga on the south-eastern side of the Baltic Sea within the context of the 'Barbarossa' invasion of the USSR (8 September/21 October 1941).
Both plans had the same objective but were based on the assumption of different start points. 'Beowulf I' was posited on rapid German victory in the Baltic states, and especially the seizure of the Kurland peninsula, as the forces of Generalfeldmarschall Wilhelm Ritter von Leeb’s Heeresgruppe 'Nord' advanced toward Leningrad. As such, this would have been a reworking of the 'Albion' operation of World War I, launched from Kurland region of Latvia. In the event, German forces were delayed as they crossed into Estonian territory.
'Beowulf II' was thus the operation actually undertaken, and was an attack from the west coast of Estonia.
'Beowulf' also involved a series of diversionary attacks ('Südwind' [ii], 'Westwind' and 'Nordwind' ), the last containing sub-plans known as 'Lel', 'Nau' and 'Stimmung') to confuse the Soviet defence.
The invasion and reduction of these Soviet-held islands in the Gulf of Riga by elements of Generaloberst Georg von Küchler’s 18th Army, with the support of the navy’s Erprobungsverbände der Ostsee (Baltic Sea trials units), was required to remove the threat that the Soviet forces on these islands would otherwise pose to the left flank of Leeb’s Heeresgruppe 'Nord' if left in Soviet hands, and also dominated the entrance to the Gulf of Finland and its seaward approaches to the city of Leningrad. Support for the ships carrying the troops was provided by a number of German warships including the light cruisers Emden, Köln and Leipzig, and these naval assets had been grouped in the Latvian ports of Liepaja, Riga, Roja and Ventspils by 10 September.
On 14 September the leading elements of Generalleutnant Helge Auleb’s 61st Division landed on Muhu, and two days later the Germans established a comparable beach-head on Saaremaa. The latter landing began with a bombardment of Finnish coast-defence ships Ilmarinen and Väinamöinen escorted by the patrol boats VMV-1, VMV-14, VMV-15 and VMV-16 as well as the icebreakers Jääkarhu and Tarmo.
The German gunnery training ship and minelayer Brummer began the attack with five patrol boats of Korvettenkapitän Drenckham’s 3rd Vorposten-Flottille, two armoured tugs, and eight assault boats.
The German torpedo boats T 2, T 5, T 8 and T 11 attacked the western side of Saaremaa, escorted by the S-boote of Korvettenkapitän Klaus Feldt’s 2nd Schnellboots-Flottille and Kapitänleutnant Friedrich Kemnade’s 3rd Schnellboots-Flottille plus nine assault boats.
From Riga, three groups totalling 50 German assault boats attacked the south coast of Muhu, and during the continuing attack, a mine sank Ilmarinen with the loss of 273 men. Finnish patrol boats rescued 132 survivors.
On 16/17 September the Soviet defenders were driven back onto the Sworbe peninsula of Saaremaa, where they became the target for a gunfire bombardment by the light cruisers Emden and Leipzig, supported by the torpedo boats T 7, T 8 and T 11. Four Soviet motor torpedo boats attempted to reach and attack the German ships, but failed.
This effectively sealed the fate of the Soviet forces on the islands in the mouth of the Gulf of Riga, and the Soviets began an evacuation to remove their remaining strength across the mouth of the Gulf of Finland to Hanko, the Soviet enclave on the south-western tip of Finland established on a 30-year lease at the end of the Soviet-Finnish 'Talvisota' in March 1940. The Soviets started to evacuate their forces from 1 November in a number of small convoys of naval vessels, and by 25 November had extracted 4,424 men, 18 tanks, 520 tons of munitions and 720 tons of rations. After the Soviet forces here had surrendered, and realising the hopelessness of their position at the throat of the Gulf of Finland after the fall of the two islands, the Soviets next evacuated their garrison in the Finnish port of Hanko on 3 December 1941, after it had been under Finnish siege since 29 June. The evacuation lasted from 29 November to 4 December.