The Phoenix breakwaters were a set of reinforced concrete caissons built as part of the artificial Mulberry harbours that were assembled as part of the preparations for the Normandy landings during World War II. A total of 213 were built, with 212 floated or side-launched. They were constructed by civil engineering contractors around the coast of Britain. They were collected at Dungeness and Selsey, and then towed by tugboats across the English Channel and sunk to form the Mulberry harbour breakwaters replacing the initial "Gooseberry" block ships. Caissons were added in the autumn of 1944 to reinforce the existing structure to cope with the harbour continuing in use longer than planned.