 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 was to comprise the flagship , the battlecruiser Moltke , along with the III Battle Squadron of the High Seas Fleet . The V Division included the four König @-@ class battleships , and was by this time augmented with Bayern . The VI Division consisted of the five Kaiser @-@ class battleships . Along with nine light cruisers , 3 torpedo boat flotillas , and dozens of mine warfare ships , the entire force numbered some 300 ships , and were 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 . 
