The Mulberry Harbour was an artificial port the size of Dover, that was prefabricated in England, and then towed across the Channel to the Normandy coast, after the D-Day landing had started. This harbour is at Arromanches, and with out it the war might have turned out differently. The design concept had a number of roots. The codename ‘Mulberry’ was simply the next available in a long list of possible code-names, so this has no significance. In 1917, when Winston Churchill was First Sea Lord during the Great War, there had been a plan for the capture of two small islands of the Dutch coastline and to use flat bottomed barges mixed with manufactured caissons to form an artificial harbour. Events moved on quickly and the idea was abandoned, yet no doubt still kept in mind for a future demand.
http://d-dayrevisited.co.uk/d-day/mulberry-harbour.html https://youtu.be/SGbMT-PQKYA