De Robeck was appointed second-in-command of the naval forces at the Dardanelles, under Vice Admiral Carden, in January 1915. De Robeck was an experienced naval officer who had served in a variety of posts at home and sea. He participated in the bombardments of the outer forts at the end of February and in the failed attempt to negotiate the minefields across the Narrows early in March. Carden’s health was damaged by the strain of these difficult operations and he was succeeded by De Robeck on 17 March 1915. On the next day, he commanded the disastrous Anglo-French assault that resulted in the destruction of three battleships and other serious loses.

De Robeck suspended all offensive action while the combined assault on Gallipoli was being prepared. De Robeck was in command of the naval side of the Gallipoli operations.