HMS Sirius was an of the British Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 which served from 1892 to 1918 in various colonial posts such as the South and West African coastlines and off the British Isles as a hastily converted minelayer during the First World War. In April 1918, Sirius was deliberately scuttled in the mouth of Ostend

Ostend

Ostend  is a Belgian city and municipality located in the Flemish province of West Flanders. It comprises the boroughs of Mariakerke , Stene and Zandvoorde, and the city of Ostend proper – the largest on the Belgian coast....

 harbour in Belgium

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 during the failed First Ostend Raid

First Ostend Raid

The First Ostend Raid was the first of two attacks by the Royal Navy on the German-held port of Ostend during the late spring of 1918 during the First World War...

. This operation was intended to block the harbour mouth and prevent the transit of German U-boats and other raiding craft from Bruges

Bruges

Bruges is the capital and largest city of the province of West Flanders in the Flemish Region of Belgium. It is located in the northwest of the country....

 to the North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

. German countermeasures were however too effective, and Sirius and its fellow blockship HMS Brilliant

HMS Brilliant (1891)

HMS Brilliant was an Apollo class cruiser of the British Royal Navy which served from 1893 to 1918 in various colonial posts and off the British Isles as a hastily converted minelayer during the First World War. In April 1918, Brilliant was deliberately scuttled in the mouth of Ostend harbour in...

were eventually destroyed by their crews outside the harbour mouth after running aground on a sandbank. The wrecks were broken up after the war.