The Dardanelles campaign was a

naval operation. (also known as the Gallipoli Campaign)

To begin with, the Dardanelles is a narrow, natural strait, internationally important, that separates Asian Turkey from European Turkey. The Dardanelles is 61 kilometres (38 mi) long, and 1.2 to 6 kilometres (0.75 to 3.73 mi) wide, averaging 55 metres (180 ft) deep with a maximum depth of 103 metres (338 ft)

From February 1915 to January 1916 (First World War) ships of the Royal Navy, French Marine nationale, Imperial Russian Navy and the Royal Australian Navy, attempted to force the defences of the Dardanelles Straits. It all began as a naval operation but the success of the Ottoman defence led to the Gallipoli/Dardanelles Campaign, an attempt to occupy the Gallipoli peninsula with land forces supported by the navies, to open the sea route to Constantinople. The Allies also tried to pass submarines through the Dardanelles to attack Ottoman shipping in the Sea of Marmara.