The partially completed Mulberry A harbour at Omaha Beach was damaged on 19 June by a violent storm that arrived from the northeast before the pontoons were securely anchored.

After three days the storm finally abated and damage was found to be so severe that the harbour was abandoned and the Americans resorted to landing men and material over the open beaches.

Thus, the Mulberries were created to provide the port facilities necessary to offload the thousands of men and vehicles and millions of tons of supplies necessary to sustain Operation Overlord.

With the planning of Operation Overlord at an advanced stage by the summer of 1943, it was accepted that the proposed artificial harbours would need to be prefabricated in Britain and then towed across the English Channel.

On 2 September 1943 the Combined Chiefs of Staff estimated that the artificial ports (Mulberries) would need to handle 12,000 tons per day, exclusive of motor transport, and in all weathers.

The caissons were built at a number of locations, mainly existing ship building facilities or large beaches, like Conwy Morfa, around the British coast.

The works were let out to commercial construction firms, including Wates Construction, Balfour Beatty, Henry Boot, Bovis & Co, Cochrane & Sons, Costain, Cubitts, French, Holloway Brothers, John Laing & Son, Peter Lind & Company, Sir Robert McAlpine, Melville Dundas & Whitson, Mowlem, Nuttall, Parkinson, Halcrow Group, Pauling & Co. and Taylor Woodrow.

[3] On completion they were towed across the English Channel by tugboats[4] to the Normandy coast at only 8.0 kilometres per hour (4.3 kn) and assembled, operated and maintained by the Corps of Royal Engineers, under the guidance of Reginald D. Gwyther, who was appointed CBE for his efforts.

(On New Year's Eve 1943, the 712th Survey Flotilla carried a Combined Operations Pilotage Party (COPP) to the Gold Beach area just west of Ver-sur-Mer.

Two soldiers – Major Logan Scott-Bowden, of the Royal Engineers, and commando Sergeant Bruce Ogden Smith, of the East Surrey Regiment – landed on the beach at night in Operation KJH and took samples of the sand.

This operation was to check the load-bearing capabilities of sand and help determine whether armoured vehicles would be able to cross the beach or become bogged down, rather than being in connection with the Mulberry harbours.)

The final Mulberry harbour survey, Operation Bellpush Charlie, occurred on the night of 30–31 January but limited information was gathered due to fog and because German lookouts heard the craft.

[6] Churchill issued his memo "Piers for use on beaches" on 30 May 1942, apparently in some frustration at the lack of progress being made on finding a solution to the temporary harbour problem.

In July 1943 a committee of eminent civil engineers consisting of Colin R White (chairman), J D C Couper, J A Cochrane, R D Gwyther and Lt. Col. Ivor Bell was established to advise on how a number of selected sites on the French coastline could be converted into sheltered harbours.

The pier designs were by: The western side of Wigtown Bay, in the Solway Firth, was selected for the trials as the tides were similar to those on the expected invasion beaches in Normandy, a harbour was available at Garlieston, and the area's remoteness would simplify security matters.

The final choice of design was determined by a storm during which the "Hippos" were undermined causing the "Crocodile" bridge spans to fail and the Swiss roll was washed away.

In the planning of Operation Neptune the term Mulberry "B" was defined as "an artificial harbour to be built in England and towed to the British beaches at Arromanches".

Corncobs were 61 ships that crossed the English Channel (either under their own steam or towed) and were then scuttled to act as breakwaters and create sheltered water at the five landing beaches.

The ships used for each beach were: Phoenixes were reinforced concrete caissons constructed by civil engineering contractors around the coast of Britain, collected and sunk at Dungeness in Kent and Pagham Harbour in West Sussex prior to D-Day.

[18] A span from Mulberry B reused after the war at Pont-Farcy was saved from destruction in 2008 by Les Amis du Pont Bailey, a group of English and French volunteers.

War work by the Butterley Company included the production of steel "pontoons used to support the floating bridge between the offshore Mulberry Harbour caissons and the shore on Gold and Omaha beaches after D-Day 1944".

[19] Roy Christian wrote: "The workers who made mysterious floats had no idea of their ultimate purpose until one morning in June 1944 they realised that their products were helping to support the Mulberry Harbour off the low coastline of Normandy, and by that time they were busy building pontoon units and Bailey bridge panels ready for the breakthrough into Germany.

An original Kite anchor is displayed in a private museum at Vierville-sur-Mer while a full size replica forms part of a memorial to Beckett in Arromanches.

[23] Then on the afternoon of 6 June 1944 (D-Day) over 400 towed component parts (weighing approximately 1.5 million tons) set sail to create the two Mulberry harbours.

The entire harbour at Omaha was deemed irreparable, 21 of the 28 phoenix caissons were completely destroyed, the bombardons were cast adrift and the roadways and piers lay smashed.

[27] The Royal Engineers had built a complete Mulberry Harbour out of 600,000 tons of concrete between 33 jetties, and had 10 mi (16 km) of floating roadways to land men and vehicles on the beach.

"However, in the critical early stage of the operation, had the Allied assault ships been caught in the open without the benefit of any protection, the damage in the American sector especially could have been catastrophic to the lines of supply and communication.

"[30] Mulberry B was substantially reinforced with units salvaged from the American harbor and that the Phoenixes were pumped full of sand to give them greater stability, measures that undoubtedly explain the extended service which the British port was able to render.

The tremendous tonnage capacities subsequently developed at both Utah and Omaha were without doubt one of the most significant and gratifying features of the entire Overlord operation.

[49] In the period between postponement and cancellation of Operation Sea Lion, the invasion of the United Kingdom, Germany developed some prototype prefabricated jetties with a similar purpose in mind.