'Mulberry' was an Allied pair of temporary harbours created off the Normandy assault beaches of 'Neptune' (iii) to facilitate the offloading of Allied cargo onto the beach in an area where there were no existing ports for the Allies to capture and press into operation (June 1944/January 1945).
Each the size of port of Dover in south-eastern England, these harbours were prefabricated in a multitude of sections and sub-assemblies, and was towed across the English Channel from southern England for assembly off the Normandy coast.
The 'Jubilee' operation of August 1942 against Dieppe had revealed that it would be foolish for the Allies to rely on the assault capture of a major port on the north coast of France, so the 'Mulberry' harbours were designed to provide the port facilities required for the offloading of the many thousands of men and vehicles, and vast tonnage of supplies necessary to nourish the Allied operations in Normandy.
The exact identity of the 'Mulberry' concept’s originator is disputed, but among those who are known to have proposed something along these lines are Hugh Iorys Hughes, a Welsh civil engineer who submitted initial plans on the idea to the War Office, Professor J. D. Bernal, a scientific adviser to the Combined Operations Headquarters, and Commodore J. Hughes-Hallett, commander of the Channel Assault Force. At a meeting after the 'Jubilee' assault on Dieppe, in which he had commanded the naval element, Hughes-Hallett had declared that if a port could not be captured, then the invading forces would have to take one with them.
The 'Mulberry' concept began to take shape when Hughes-Hallett moved to be naval chief-of-staff to the 'Neptune' (iii) and 'Overlord' planners. Developed by Bernal and Brigadier Bruce White, with the enthusiastic approval of Prime Minister Winston Churchill, the harbours were based on many bulky caissons of various sorts to allow the construction of breakwaters and piers, and of connecting structures to provide the roadways. The caissons were built at a number of locations around the British coast and then towed slowly to the Normandy coast.
By 9 June, only three days after D-Day, the 'Mulberry A' and 'Mulberry B' harbours had been constructed at St Laurent sur Mer on the US 'Omaha' Beach and Arromanches on the British 'Gold' Beach respectively. In the period 19/22 June a large storm effectively destroyed the US harbour on 'Omaha' Beach, leaving only the British 'Golden Arrow' harbour, which came to be known as Port Winston, at Arromanches. While the harbour at Omaha Beach was destroyed sooner than expected, largely as a result of the fact that it was not firmly anchored to the sea bed, 'Golden Arrow' saw considerable use for eight months despite the fact that the harbours had been designed to last for only three months.
By D+100, 'Golden Arrow' had made it possible for more than 2.5 million men, 500,000 vehicles, and more than 4 million tons of supplies to be landed, thereby providing much needed reinforcement for the Allied forces in France.
A complete 'Mulberry' used 600,000 tons of concrete in the creation of a harbour with 33 jetties, and had 10 miles (16 km) of floating roadways to land men and vehicles from ships onto the beach.
The designations of the harbours' main elements included 'Corn Cob' block ships which crossed the Channel under their own steam or under tow before being scuttled to become 'Gooseberry' units providing sheltered water at the five landing beaches, 'Bombardon' floating outer breakwaters, 'Phoenix' reinforced concrete caissons, 'Whale' floating piers and 'Spud' pier heads.
The 'Phoenix' reinforced concrete caissons were constructed by civil engineering contractors around the British coast, collected and sunk at Dungeness, the Cant and Selsey Bay, and then refloated at the appropriate time and towed across the Channel to form, with the 'Gooseberry' block ships, the breakwaters for the 'Mulberry' harbours. The 'Whale' piers were the roadways that connected the 'Spud' pier heads with the land, and their roadways were made from Bailey bridge type units that had a span of 80 ft (24.5 m) mounted on pontoon units called 'Beetles'. The 'Spud' pier heads or landing wharves were the locations at which ships were unloaded. Each of these consisted of a pontoon with four legs that rested on the sea bed to anchor the pontoon, yet allowed it to float up and down freely with the tide.