Three years later, the ship was mobilized in August 1914 following the outbreak of World War I and assigned to III Scouting Group, serving initially with the High Seas Fleet in the North Sea. There, she escorted the main German fleet during the raid on Yarmouth in November and the raid on Scarborough, Hartlepool and Whitby in December, though she saw no action during either operation. She was transferred to the Baltic Sea in April 1915 and took part in several operations against Russian forces, including the successful attack on Libau in May and the failed attack on Riga in August. The threat of British submarines convinced the German command to withdraw old vessels like "Roon" by early 1916, and she was again decommissioned and eventually used as a training ship. Plans to convert her into a seaplane tender in 1918 came to nothing with the end of the war, and she was broken up in 1921.