The start of the First World War saw Jeans's ship engaged in convoy work between Bombay and Aden. Then he saw service in the Turkish attempt to take the Suez Canal, in the bombardment of Smyrna. He also took part in the attempt to force the passage of the Dardanelles, and dealt with the large number of wounded brought off from the attempts to force a beachhead in the Landing at Cape Helles.