With the initial bombardments over and the arrival of the transport fleet it became necessary to secure Tagga Bay as quickly as possible. During the course of the morning it had become clearly evident that there were Russian mine barriers in areas hitherto thought safe, and therefore the chief of the II Minesweeper Flotilla was ordered to immediately begin sweeping work. Before noon the 8th Minesweeper Half Flotilla (8 MSHF) initiated a search-sweep of Tagga Bay and simultaneously began work to sweep the barrier where Corsica had been damaged. This barrier consisted of small, cylindrical, very rusty mines with three lead horns each. Next the area between Cape Ninnast and Cape Pank was swept. The 3rd Minesweeper Half Flotilla collected the III Battle Squadron and then the IV Battle Squadron and delivered them to Tagga Bay, whilst 4 MSHF collected Bayern. By 1700hrs all the heavy ships were safely anchored in Tagga Bay.
The security of Tagga Bay against submarines was the responsibility of the Net Barrier Unit of the Baltic, under the command of Korvettenkapitän Kaulhaussen. It was the first occasion that the nets were being used offensively on the enemy coast. It was planned to lay a double net square across the mouth of the bay from Cape Ninnast to Cape Hundsort, with a total length of 12 kilometers. Two gaps, which would be closed at night, would allow ships to enter and exit the bay. By 0930hrs on 12 October the net layer Rossal began laying the western part of the net, whilst an hour later Eskimo began the eastern wing. By 1550hrs Rossal had concluded her work whilst Eskimo finished her sequence at around 1900hrs. For further security against submarines a ‘listening line’ was established between Hundsort and Dagerort. This consisted of a series of trawlers fitted with hydrophones laid out at intervals.
Meanwhile the 2nd Gruppe of the 1st S-Half Flotilla were working to secure a route into Soelo Sound, which separated Dago from Ösel. Control of the Soelo sound was particularly important because the Russians could use this passage to mount a destroyer attack on the German flank. Therefore, possession of the sound was a prime consideration for the Germans, both to prevent Russian destroyer attacks and also to provide support for troops ashore, particularly those who were to take the stone dam which ran from Ösel to Moon Island. Already before dawn the A28 and her drifters had pressed forward, sweeping for mines and taking soundings as they went. When Bayern and Emden opened fire on Battery No 34 at Serro, the Russians responded by taking A28 and her boats under fire. Seven salvoes landed amongst the S-Flotilla and A28 was hit, as previously mentioned; however, after that fire was ceased. The small torpedoboat and drifters resumed their advance and succeeded in locating the narrow, buoyed channel. Whilst conducting this work, at 0812hhrs, the battery at Serro reopened fire for a short time, but was again brought to silence by Bayern. With that the I FdT dispatched S61 and S63 to silence the battery permanently, which they did during the course of the morning by landing a commando of men who removed the locks from the cannon.
After the channel through Soelo Sound had been located, the lead boat of the 2nd S-Half-Flotilla, T130, and three sweeper boats pushed forward into the Kassar Wiek, to bombard the wireless station at Pawasterort. The passage through the Soelo Sound was particularly treacherous, with many uncharted rocks and strong, difficult currents. However, even the largest Russian destroyers had utilized this passage previously for operations. Now the small German unit penetrated into the Kassar Wiek, which aerial reconnaissance had reported clear of Russian ships. Ominously, a smoke cloud soon became conspicuous to the east.
With the receipt of the first news of the appearance of enemy forces off Tagga Bay, the commander of the Naval Forces of the Riga Gulf, Vice Admiral Bakhirev, ordered all units to be at a state of half hour readiness and to refill their stocks of coal and oil. The greater part of the torpedoboats had participated in the production of defensive mine barriers off Pernau the previous day. The duty torpedoboats which were waiting in readiness, General Kondratenko and Pogranitschnik, under the command of the chief of the IV Division Torpedoboat-Destroyers, Captain 1st Rank Postelnikov, were ordered to conduct reconnaissance on the Kassar Wiek. The gunboat Grozyashchi was in Rogekul for minor maintenance and Vice Admiral Bakhirev ordered her to go to the Kassar Wiek and place herself at the disposal of the IV Division chief.
At 0930hrs Captain 1st Rank Postelnikov reported the German torpedoboats in Soelo Sound. General Kondratenko opened fire and forced the German unit to retire back into the Soelo Sound. The two Russian destroyers followed but were taken under fire by Emden at a range of 15,800 metres, and subsequently moved off to the east, out of range.
Meanwhile, ashore, the Germans were making rapid progress. The cyclist company under Hauptmann von Winterfeld was nearing Orrisar by noon and support for them from inside the Kassar Wiek was assuming greater importance. For the time being the I FdT only had Fregattenkapitän von Rosenberg’s T144 and six A-Boats available to support the infantry, and Winterfeld thereby determined to postpone any advances until after Kapitänleutnant Zander arrived with the remainder of 13th Torpedoboat Half Flotilla. When he arrived at 1330hrs, Kapitänleutnant Zander was immediately ordered to push the Russian destroyers to the east to allow von Rosenberg to push through the southern Kassar Wiek towards Keinast, the westerly part of Moon.
As the Russian destroyers moved east they were joined by the large torpedoboat-destroyer Desna, with the chief of the torpedoboat divisions, Rear Admiral Stark, aboard. He had been en route to Rogekul to find the state of readiness of the destroyers there when he received the wireless message from the commander of the IV Division Torpedoboat-Destroyers (IV Div TBD) about the appearance of the enemy. Rear Admiral Stark was given material recovered from a crashed German reconnaissance floatplane, which included maps and other material. Then, since the Germans no longer seemed to threaten, and the gunboat Grozyashchi had meanwhile approached, Desna made off to the east. At around 1400hrs, IV Div TBD was four nautical miles east of Serro as Grozyashchi approached and thereon the division chief ordered her to open fire on the German vessels with her long-range cannon. Shortly afterwards, at 1430hrs, the five torpedoboats of the 13 TBHF passed into Soelo Sound. The commander of Grozyashchi, Captain 2nd Rank Ordovski-Tanaevski, decided to utilize the disadvantageous situation of the Germans, manoeuvring in the narrow and fractious sea channel, to best advantage and he took course west and opened fire at 1426hrs at a range of 70 cable-lengths, or 12,800 metres. The fourth and fifth salvos straddled the Germans who immediately developed a smoke screen. Shortly afterwards the five torpedoboats of 13 TBHF emerged from the smoke at high speed. However, the Russian gunboat was not supported by the destroyers and at 1440hrs the division chief ordered Grozyashchi to return to the destroyers, which she did whilst continuing to fire from her stern guns. This allowed the German torpedoboats to negotiate Soelo Sound and deploy into the Kassar Wiek. To get to within effective range, 13 TBHF made a sudden dash forward at high speed and then deployed onto a course for a firing position and opened fire. This manoeuvre was repeated four times.