Allies' own war effort. World War I By 1917 the Imperial Navy had amassed a fleet of 55 submarines, used to varying degrees of success. Baltic Sea In the Baltic Sea, Germany and Russia were the main combatants, with a number of British submarines sailing through the Kattegat to assist the Russians, including commanded by Max Horton. With the German fleet larger and more modern (many High Seas Fleet ships could easily be deployed to the Baltic via the Kiel Canal when the North Sea was quiet), the Russians played a mainly defensive role, at most attacking convoys between Germany and Sweden and laying offensive minefields. Russian and British submarines attacked German shipping sailing between Sweden and Germany. With heavy defensive and offensive mining on both sides, fleets played a limited role on the Eastern Front. The Germans mounted major naval attacks on the Gulf of Riga, unsuccessfully in August 1915 and successfully in October 1917, when they occupied the islands in the Gulf (Operation Albion) and damaged Russian ships departing from Riga (Battle of Moon Sound), which had recently been captured by Germany. By March 1918, the Russian Revolution and the Treaty of Brest-Litovsk made the Germans masters of the Baltic sea and German fleets transferred troops to support newly independent Finland and to occupy much of Russia, halting only when defeated in the West. The Russians evacuated the Baltic fleet from Helsinki and Reval to Kronstadt during the Ice Cruise of the Baltic Fleet in March 1918. Black Sea The Black Sea was the domain of both the Russian and Ottoman Empires but the Russian fleet dominated the sea. It possessed a large fleet based in Sevastopol and it was led by two skilled commanders: Admiral Eberhart and Admiral Kolchak (who took over in 1916). The war in the Black Sea started when the Ottoman fleet bombarded several Russian cities in October 1914. The most advanced ships in the Ottoman fleet consisted of just two German ships: the battlecruiser and light cruiser , both under the command of Admiral Wilhelm Souchon. Goeben was damaged on at least four occasions and was usually chased back to port by the superior Russian Navy. By the end of 1915, the Russian fleet had nearly complete control of the sea. The Black Sea fleet was used mainly to support General Yudenich in his Caucasus Campaign. For example, in August 1915, a Russian