The naval operations in the Dardanelles campaign (17 February 1915 – 9 January 1916) took place against the Ottoman Empire during the First World War. Ships of the Royal Navy, French , Imperial Russian Navy () and the Royal Australian Navy, attempted to force a passage through the Dardanelles Straits, a narrow, waterway connecting the Mediterranean Sea with the Sea of Marmara and the Black Sea further north. The Ottoman defence and in particular their naval mines defeated the naval operation. The Allies conducted an invasion of the Gallipoli peninsula to clear the area of Ottoman artillery for a resumption of the naval operations. The Allies also tried to pass submarines through the Dardanelles to attack Ottoman shipping in the Sea of Marmara. Background Dardanelles Strait The mouth of the strait is wide with a rapid current emptying from the Black Sea into the Aegean. The distance from Cape Helles to the Sea of Marmara is about , overlooked by the heights on the Gallipoli peninsula and lower hills on the Asiatic shore. The passage widens for to Eren Keui Bay, the widest point of the strait at , then narrows for to Kephez Point, where the waterway is wide and then broadens as far as Sari Sighlar Bay. The narrowest part of the strait is upstream, from Chanak to Kilid Bahr at , where the channel turns north and widens for to Nagara Point. From the point, the passage turns north-east for the final to the Sea of Marmara. The Ottomans used the term "fortress" to describe the sea defences of the Dardanelles on both sides of the waterway from the Aegean approaches to Chanak. In 1914 only the defences from the entrance of the straits and from the north end of Kephez Bay to Chanak had been fortified. Until late October 1914, the nature of the seaward defences of the Dardanelles was known to the British and French but after hostilities commenced, information on improvements to the Ottoman fortifications became harder to obtain. Ottoman entry into the war At the beginning of the 20th century, the Ottoman Empire had a reputation as the sick man of Europe. After the Balkan Wars of 1912 and 1913, the French, British and Germans had offered financial aid. In December 1913, the Germans sent a military mission to Constantinople, headed by General Otto Liman von Sanders. The geographical position of the Ottoman