In early September 1917, following the German conquest of the Russian port of Riga, the German navy decided to evict the Russian naval forces that still held the Gulf of Riga. To this end, the Admiralstab (the Navy High Command) planned an operation to seize the Baltic islands of Ösel, particularly the Russian gun batteries on the Sworbe peninsula. On 18 September, the order was issued for a joint Army-Navy operation to capture Ösel and Moon islands; the primary naval component consisted of the flagship Moltke and III Battle Squadron of the High Seas Fleet. At this time, V Division included the Bayern and four König-class battleships. VI Division consisted of the five Kaiser-class battleships. Along with 9 light cruisers, 3 torpedo boat flotillas, and dozens of mine warfare ships, the entire force numbered some 300 ships, supported by over 100 aircraft and 6 zeppelins. The invasion force amounted to approximately 24,600 officers and enlisted men. Opposing the Germans were the old Russian pre-dreadnoughts Slava and Tsesarevich, the armored cruisers Bayan, Admiral Makarov, and Diana, 26 destroyers, and several torpedo boats and gunboats. The garrison on Ösel numbered some 14,000 men.The operation began on 12 October, when Bayern, along with Moltke and the four Königs, began firing on the Russian shore batteries at Tagga Bay. Simultaneously, the five Kaisers engaged the batteries on the Sworbe peninsula; the objective was to secure the channel between Moon and Dagö islands, thus blocking the only escape route of the Russian ships in the gulf. Bayern's role in the operation was cut short when she struck a naval mine at 5:07 while moving into her bombardment position at Pamerort. The mine explosion killed one Unteroffizier and six sailors, allowed 1,000 metric tons (980 long tons; 1,100 short tons) of water into the ship and caused the forecastle to sink by 2 m (6.6 ft). Despite the damage inflicted by the mine, Bayern engaged the naval battery at Cape Toffri on the southern tip of Hiiumaa. Bayern was released from her position at 14:00. Preliminary repairs were made on 13 October in Tagga Bay. The temporary repairs proved ineffective, and Bayern had to be withdrawn to Kiel for repairs; the return trip took 19 days. Repairs lasted from 3 November to 27 December, during which the forward torpedo tube room was stripped of its equipment and the torpedo ports were sealed. The room was then turned into an additional watertight compartment. Four 8.8 cm (3.5 in) SK L/30 anti-aircraft guns were also installed during the repairs.On 16 October, two König-class battleships and several smaller vessels were sent to engage the Russian battleships in the Gulf of Riga. The following day, König and Kronprinz engaged the Russian battleships—König dueled with Slava and Kronprinz fired on both Slava and the cruiser Bayan. The Russian vessels were hit dozens of times, until at 10:30 the Russian naval commander, Admiral Bakhirev, ordered their withdrawal. Slava had taken too much damage, and was unable to escape; instead, she was scuttled and her crew was evacuated on a destroyer. By 20 October, the naval operations were effectively over; the Russian fleet had been destroyed or forced to withdraw, and the German army held the islands in the gulf.

Question: What, specifically, did the Admiralstab plan to seize from the Russians?
Answer: Baltic islands of Ösel, particularly the Russian gun batteries on the Sworbe peninsula

Question: Approximately how many destroyers were the Germans up against?
Answer: 26