 In early September 1917 , following the German conquest of the Russian port of Riga , the German navy decided to eliminate the Russian naval forces that still held the Gulf of Riga . The <unk> ( Navy High Command ) planned an operation to seize the Baltic island of Ösel , and specifically the Russian gun batteries on the <unk> Peninsula . On 18 September , the order was issued for a joint operation with the army to capture Ösel and Moon Islands ; the primary naval component was to comprise the flagship , Moltke , along with the III and IV Battle Squadrons of the High Seas Fleet . The II Squadron consisted of the four König @-@ class ships , and was by this time augmented with the new battleship Bayern . The IV Squadron consisted of the five Kaiser @-@ class battleships . Along with nine light cruisers , three torpedo boat flotillas , and dozens of mine warfare ships , the entire force numbered some 300 ships , supported by over 100 aircraft and six <unk> . The invasion force amounted to approximately 24 @,@ 600 officers and enlisted men . 
