Mulberry Harbours were massive temporary portable harbours developed and made in the UK for the D-Day landings, and towed across the English Channel to enable the rapid offloading of absolutely vast numbers of vehicles and other cargo to the Normandy beaches in June, 1944. It is fair to say – that the invasion would not have succeeded without them – even though one of them at some point eventually collapsed into the very rough and turbulent seas.
These can be seen from the back of the D-Day Centre.