Phoenix breakwaters
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The Phoenix breakwaters were a set of reinforced concrete caissons constructed by civil engineering contractors around the coast of Britain in World War II. They were collected and sunk at Dungeness, the Cant, and Selsey Bay, and then towed across the English Channel to form the Mulberry harbour breakwaters together with the 'Gooseberry' block ships.
Several Phoenix breakwaters are still in use in Britain: two are part of the harbour off Castletown at Portland Harbour and one can be dived in 10 metres of water off Selsey Bill. There is also a smaller Mulberry in Langstone Harbour.