​​​The harbours were built secretly in the United Kingdom and towed across the channel from D-Day. Construction then began in the days following the successful landing of the Allies. 

​​The conception and execution of the ‘Mulberry’ harbours was unique, and each one covered an area larger than Dover port (England). Supreme Commander (General Eisenhower) ordered that the harbours must provide sheltered water by 10 June 1944 and be fully established by 20 June. 

​​The total daily target disembarkation figures for the two harbours were 3,000 tonnes of stores by 10 June, 7,000 tonnes and 2,500 vehicles by 14 June, and finally 12,000 tonnes and 2,500 tonnes of unwaterproofed vehicles. The artificial harbours were designed to last 90 days, and their parts could be towed and erected in force 4 gales. 

​The main components of the harbours were: ‘Phoenix’ the outer break waters, ‘Bombardons’ for mooring points, and ‘Whale’ the floating roads. The remains of ‘Phoenix’ and ‘Whales’ can still be seen on the beach and at sea today. ‘Bombardons’ and ‘Phoenix’ were towed from Portland (Island off the southern English coast) and by the morning of 10 June were being put into position off Arromanches. Decommissioned ships were sunk off the coast beyond the outer wall of the artificial harbour, known as ‘Gooseberry’, and offered shelter to ships and craft. By the afternoon of 10 June, they were all in place. These are no longer visible today. 

​​By 14 June, all ‘Phoenix’ had been sunk and were completed. By 16 June all ‘Whales’ were in place and the harbours were taking shape. The pier head for unloading the Landing Crafts had been connected to allow the unloading of vessels. 

​Due to the importance of the harbours, a heavy anti-aircraft defence protected them from an early stage. This consisted of light and heavy guns located on shore and out at sea. Additionally, 60 trawlers fitted with ‘Esso’ generators provided smoke screens to help mask the construction from German observations. 

The harbour at Arromanches-les-Bains was referred to as ‘Mulberry B’. It was also known as ‘Port Winston’, after British wartime Prime Minister Winston Churchill.