In April 1918, "Sirius" was deliberately scuttled in the mouth of Ostend harbour in Belgium during the failed First Ostend Raid. This operation was intended to block the harbour mouth and prevent the transit of German U-boats and other raiding craft from Bruges to the North Sea. German countermeasures were however too effective, and "Sirius" and her fellow blockship were eventually destroyed by their crews outside the harbour mouth after running aground on a sandbank. The wrecks were broken up after the war.