On June 5, 1944, General Dwight D. Eisenhower, the Allied Supreme Commander, authorized Operation Neptune after a 24-hour delay due to bad weather. This operation marked the largest seaborne invasion in history, initiating the D-Day landings on June 6, 1944, known as Operation Overlord.

Early in the morning, 24,000 British and American paratroopers departed from southern England to their targets in Nazi-occupied France. The first Horsa gliders landed near Pegasus Bridge at 12:16 AM, and at 5:50 AM, warships bombarded the Normandy beaches.

The initial landings at beaches codenamed Utah, Omaha (by Americans), and Gold, Juno, Sword (by British and Canadians) began at 6:30 AM. Omaha Beach saw the highest casualties, with more than 2,000 American fatalities. Despite severe hardships, including underwater hazards and fortified German defenses, 130,000 troops landed successfully by the end of the day.

The invasion was supported by a massive deception operation to mislead German forces about the landing locations. Operation Overlord followed increased pressure from Soviet leader Josef Stalin for a second front to alleviate the Eastern Front.

Significant groundwork was laid by scientists and engineers, including Jack Darbyshire from Blaenau Ffestiniog, who developed methods to predict wave conditions crucial for the landing timing. Additionally, Hugh Iorys Hughes of Bangor devised the Mulberry Harbours, essential for maintaining supplies post-landing.

The landings provided the Allies a critical foothold in northern France. After intense fighting, Operation Cobra allowed US armored divisions to break through German defenses by late July. By August, Allied forces liberated Paris, leading to continued advances until Germany’s surrender in May 1945.