On 28 April, British forces attempted to block the canal at Zeebrugge and bottle up the vessels of the Flanders Flotilla in the Zeebrugge Raid. In the raid, the British succeeded in sinking two obsolete cruisers, and , in the narrowest part of the canal. British admiral Roger Keyes, who had planned the raid, believed that the Flanders Flotilla ships were bottled up for a long period of time. However, the following day, after the Germans had removed two piers, "UB-16"—under "Oblt." Vicco von der Lühe, her newest commander—made the first sortie from Zeebrugge after the raid.