During the First World War Gough-Calthorpe initially served as commander of the 2nd Cruiser Squadron of the Grand Fleet, then became Second Sea Lord and after that became Admiral commanding the Coastguard and Reserves. In the closing years of the War he served as Commander-in-Chief of the Mediterranean Fleet, in which capacity he signed the Armistice of Mudros on behalf of all the Allies, by which the Ottoman Empire accepted defeat and ceased hostilities. The Occupation of Constantinople began with the Allied fleet entering Constantinople in November 1918 and it was Gough-Calthorpe's flagship, , that led the way.