On 23 April 1918 the British enacted a raid on the Zeebrugge mole, a long concrete harbour wall which reached into the sea from the Belgian town. The purpose of the raid was to block the ports of Ostend and Zeebrugge, which the Germans were using as submarine bases. The cruiser HMS Vindictive and the repurposed Mersey ferries Daffodil and Iris II were deployed to land Royal Marines on the mole so that they could distract the Germans and destroy shore batteries. Meanwhile, three old British cruisers filled with concrete were to be scuttled at the narrow entrance of the Zeebrugge harbour. When they exploded and damaged the mole, pieces of concrete were flung over a wide area and this piece landed on a fender on HMS Vindictive.