 To block Bruges , Keyes and Lynes decided to conduct two raids on the ports through which Bruges had access to the sea . Zeebrugge was to be attacked by a large force consisting of three blockships and numerous supporting warships . Ostend was faced by a similar but smaller force under immediate command of Lynes . The plan was for two obsolete cruisers — HMS Sirius and Brilliant — to be expended in blocking the canal which emptied at Ostend . These ships would be stripped to essential fittings and their lower holds and ballast filled with rubble and concrete . This would make them ideal barriers to access if sunk in the correct channel at the correct angle . 
