Mulberry harbours were two temporary portable harbours developed by the British Admiralty and War Office during the Second World War to facilitate the rapid offloading of cargo onto beaches during the Allied invasion of Normandy in June 1944. Designed in 1942 and then built in under a year in great secrecy, within hours of the Allies successfully creating beachheads following D-Day, sections of the two prefabricated harbours and old ships, to be sunk to create breakwaters, were being towed across the English Channel from southern England and placed in position off Omaha Beach and Gold Beach.

The Normandy landings were the landing operations and associated airborne operations on Tuesday, 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during World War II. Codenamed Operation Neptune and often referred to as D-Day, it is the largest seaborne invasion in history. The operation began the liberation of France, and the rest of Western Europe, and laid the foundations of the Allied victory on the Western Front.