The Mulberry Harbours were floating portable harbours developed and built by the British during the Second World War. After the Normandy beachheads were successfully held by the Allies following the D-Day invasion of Tuesday June 6th 1944, two prefabricated concrete harbours were floated in sections across the English Channel and assembled off 'Omaha' beach (Mulberry A) and 'Gold' beach (Mulberry B). Once in place, they made possible the offloading of cargo onto the beaches. The Normandy Landings (codenamed Operation Neptune) remain the largest seaborne invasion in history.