Winston Churchill  addressed the problem in a May 30, 1942, memo: Piers for Use on Beaches. . . . must float up and down with the tide. . . . Let me have the best solution. . . . Don't argue the matter. The difficulties will argue for  themselves.

The artificial harbours were secretly built in parts -- which German intelligence mistakenly took to be for blocking their seaports, and towed into position by U.S. merchant seamen in a flotilla of tugs, where they were sunk in place.

In combination these harbours would be twice the size of Gibraltar. Through them in a few days would pass the men and machines of history's greatest amphibious operation--156,000 men with all their trucks and tanks and artillery pieces, and food and fuel and ammunition.

Tempestuous weather postponed D-Day until June 6. The enormous harbours to land the seaborne invasion began to take shape.  During the few days of their construction Allied troops stormed the beaches  with heavy air cover and artillery support from warships in the channel.

Each Mulberry Harbour was in essence floating reinforced concrete blocks.  joined together to form 2 separate harbours  stretching some 9.5 Kilometres in length. To anchor these harbours into position it was necessary to sink 59 merchant ships to guard against the harbours from being broken up in rough weather.

Garlieston is a coastal resort and port on Whithorn Bay. The port was used as a practice ground for the Mulberry harbour used in D-Day Landing. Garlieston is the nearest Scottish port to the Isle of Man.