 <unk> the Germans were the old Russian pre @-@ dreadnoughts <unk> and <unk> , the armored cruisers Bayan , Admiral <unk> , and Diana , 26 destroyers , and several torpedo boats and gunboats . Three British C @-@ class submarines where also stationed in the Gulf . The <unk> Strait , the main southern entrance to the Gulf of Riga , was heavily mined and defended by a number of coastal artillery batteries . The garrison on Ösel numbered nearly 14 @,@ 000 men , though by 1917 it had been reduced to 60 to 70 percent strength . 
