With heavy defensive and offensive mining on both sides, fleets played a limited role in 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 and damaged Russian ships departing from the city of Riga, recently captured by Germany. This second operation culminated in the one major Baltic action, the battle of Moon Sound at which the Russian battleship was sunk.