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Mulberry was the codename given to the artificial, temporary harbours developed to supply the Allies after the D-Day invasion of France during WWII.
The Mulberry Harbour breakwater was constructed in sections in England and floated out for assembly at Arromanches off the French coast. For the first time in history an invading army took its own harbour to the enemy-held shore.
The colossal task of planning and constructing the harbour was carried out between June 1943 and June 1944. Halcrow were joint consulting engineers for the work.
Construction and experiment had to proceed concurrently because of limited time. Two prefabricated ports would be built, one for the British sector and one for the American, each consisting of a breakwater formed from concrete caissons (codename Phoenix). In order to take the enormous shipping traffic necessary to sustain Operation Overlord and the Battle of Normandy each harbour had to be the same size as Dover. This entailed the construction of 150 Phoenix units.
The prefabricated ports were completed on time and towed by a fleet of 85 tugs across the Channel. The caissons, weighing 7000 tons, were sunk accurately and the ports laid out. Fifteen obsolete ships had already been sunk to form a preliminary harbour arm. On D-Day+13 a gale destroyed the American harbour but the British harbour, although damaged, continued to allow men and equipment ashore until the capture of Cherbourg took the strain off the artificial port.
The remains of the harbour in the British sector are still visible today on the beaches of Arromanches.