 The first major RAN victory of the war occurred when the cruiser , HMAS Sydney sank the German light cruiser , SMS Emden off the Cocos Islands in the Indian Ocean on 9 November 1914 . Four Australians were killed in the engagement and another 12 were wounded . Ships of the RAN helped provide naval cover for the ambitious landings at Gallipoli , and the submarine AE2 broke the blockade of the Dardanelles to harass Turkish shipping but was later sunk and her crew captured in the Sea of Marmara . 
