"Severn" had a relatively successful career during the First World War with at least three engagements. At the Battle of the Yser in 1914, off the coast of Belgium, she bombarded German troops as well as artillery positions. On 10 October 1914, she survived an attack by the submarine when a torpedo passed under the shallow draught vessel. In early 1915, the twin turret was removed and replaced by two shielded single 6 inch guns fore and aft. In July 1915, the monitor was towed to the Rufiji River delta in German East Africa where she and "Mersey" then assisted in the destruction of the German light cruiser . She continued to serve on the East Africa station until 1918 and after a long refit in Alexandria, also served on the lower Danube until March 1919.