HMS Sirius was an Apollo-class cruiser of the British Royal Navy 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.

The Naval Defence Act 1889 resulted in orders being placed for 21 second-class protected cruisers of the Apollo-class, of which, two, HMS Sirius and HMS Spartan, were ordered from Armstrong's Elswick shipyard.

She was one of 10 ships of the class that was sheathed in wood and copper to reduce fouling.

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 too effective, however, and Sirius and her sister ship and fellow blockship HMS Brilliant were eventually scuttled by their crews outside the harbour mouth on 23 April 1918 after running aground on a sandbank.