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.

Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful liberation of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 (D-Day) with the Normandy landings. A 1,200-plane airborne assault preceded an amphibious assault involving more than 5,000 vessels. Nearly 160,000 troops crossed the English Channel on 6 June, and more than two million Allied troops were in France by the end of August.