The Allied fleet's attempt to force the Dardanelles in February 1915 failed and was followed by an amphibious landing on the Gallipoli peninsula in April 1915. In January 1916, after eight months' fighting, with approximately 250,000 casualties on each side, the land campaign was abandoned and the invasion force withdrawn. It was a costly defeat for the Entente powers and for the sponsors, especially First Lord of the Admiralty (1911–1915), Winston Churchill. The campaign was considered a great Ottoman victory. In Turkey, it is regarded as a defining moment in the history of the state, a final surge in the defence of the motherland as the Ottoman Empire retreated. The struggle formed the basis for the Turkish War of Independence and the declaration of the Republic of Turkey eight years later, with Mustafa Kemal Atatürk, who rose to prominence as a commander at Gallipoli, as founder and president.