After returning to the fleet, "Derfflinger" conducted battle readiness training in the Baltic Sea for the rest of October and all of November. By this time, the Germans had abandoned offensive use of the surface fleet, favoring instead the U-boat campaign against British merchant shipping. "Derfflinger" and the rest of the fleet were used to defend German waters so the U-boats could continue to operate. During the Second Battle of Heligoland Bight in November 1917, "Derfflinger" sailed from port to assist the German light cruisers of the II Scouting Group, but by the time she and the other battlecruisers arrived on the scene, the British raiders had fled northward. On 20 April 1918, "Derfflinger" covered a minelaying operation off Terschelling.