Halcrow's most spectacular wartime achievement was the work on the Mulberry Harbour. Mulberry was the code name for the artificial, temporary harbours developed to supply the Allies after the D-Day invasion of France during the Second World War.
Halcrow were joint consulting engineers for the famous Mulberry Harbour breakwater which was constructed in sections in England and floated out for assembly at Arromanches off the French coast. So 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.
Time was short and it was not possible to carry out exhaustive tests, construction and experiment had to proceed concurrently. The plan was for two prefabricated ports, 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 plus thirteen a gale destroyed the American harbour but the British harbour, although damaged, continued to pour men and equipment ashore until the capture of Cherbourg took the strain off the artificial port.
The Mulberry Harbour is believed by many to be one of the best examples of military engineering. The remains of the harbour in the British sector are still visible today on the beaches of Arromanches.