Artificial harbor

Mulberry harbours were temporary portable harbours developed by the British during World War II to facilitate the rapid offloading of cargo onto beaches during the Allied invasion of Normandy in June 1944. After the Allies successfully held beachheads following D-Day, two prefabricated harbours were taken in sections across the English Channel from Britain with the invading army and assembled off Omaha (Mulberry "A") and Gold Beach (Mulberry "B").

The Mulberry harbours were to be used until the Allies could capture a French port; initially thought to be around three months. However although Antwerp in Belgium was captured on 4 September 1944, the Port of Antwerp was not opened until 28 November as the approaches to the port were held by the Germans until the (delayed) Battle of the Scheldt was won. Two French ports were eventually available; the port of Boulogne on 14 October after Operation Wellhit and the port of Calais in November after Operation Undergo. Montgomery insisted that the First Canadian Army clear the German garrisons in Boulogne, Calais and Dunkirk (which was held until 9 May 1945) first before the Scheldt although the French ports were "resolutely defended" and had all suffered demolitions so would not be navigable for some time. And the success of Operation Dragoon meant that the southern French ports of Marseille and Toulon were available in October.

So the need for the harbour at Gold Beach lessened only about five months after D-Day. It was used for 10 months after D-Day; and over 2.5 million men, 500,000 vehicles, and 4 million tonnes of supplies were landed at Gold Beach before it was fully decommissioned. The Mulberry harbour at Omaha Beach had been severely damaged in a storm in late June 1944 and was abandoned.

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Wikipedia