It was the largest amphibious assault ever launched, and turned the tide of the Second World War.
And 70 years since D-Day, the world's focus will return to Normandy to mark the historic invasion and the sacrifice of those who lost their lives.
The historic Allied invasion on June 6, 1944, saw more than 75,000 British, Canadian and other Commonwealth troops land on the Normandy beaches, joining with the United States and the Free French to form an Allied invasion force of more than 130,000.
Another 7,900 British troops landed by air, while the force was supported by more than 7,000 ships and smaller vessels off the coast.
The casualty numbers ran into thousands, with more than 4,000 British and Commonwealth troops left killed, wounded or missing.
But the assault established a crucial second front, turning the tide of the war and ultimately leading to an Allied victory in 1945.
The year's 70th anniversary commemorations will see the historic victory marked in both France and England, with world leaders attending a special ceremony in Normandy.
The Queen, Prime Minister David Cameron, US president Barack Obama, as well as German chancellor Angela Merkel and Russian leader Vladimir Putin will attend an international ceremony on Sword Beach.
It will be the first time the Queen has attended D-Day celebrations in France since the 60th anniversary in 2004.
The international ceremony on Sword beach is just one of many events taking place across Normandy, as well as in the UK, to mark the 70th anniversary - which comes in the same year that the centenary of the First World War begins.
On June 5, ceremonies will take place at Ranville, the first village to be liberated on D-Day, as well as at Pegasus Bridge, site of the famous assault immortalised in the film The Longest Day.
There will be a mass parachute drop by members of 16 Air Assault Brigade, and on June 6 a service of remembrance will take place at Bayeux Cathedral organised by the Royal British Legion and the Normandy Veterans Association (NVA), followed by an event at the Bayeux War Cemetery.
The NVA - whose members are making their last official pilgrimage to Normandy before the organisation disbands - is also holding a ceremony at Arromanches, where remains of the concrete Mulberry Harbour still sit.
This year will be particularly poignant, as it is the last to be officially marked by the NVA, which announced that after this June it will no longer be taking trips to France for the D-Day anniversary and plans to officially disband after the summer's events.
National Secretary George Batts, himself a D-Day veteran, said: "We've been going over there for 30/40 years on pilgrimage to honour mates we left behind.
"This is our final one literally because of age. It's inevitable that we have got to pack up.
"At one time we had about 13-14,000 members of the association and we are now at less than 600.
"At our age we are losing them regularly unfortunately, but it means a hell of a lot going over there because it cements the friendships we made when we were in Normandy.
"Sometimes when you go to these events you see somebody that you know and you only see them once a year but the friendship is still there."
Mr Batts said some veterans might still attend in future years, and they would still meet up, but there would be no official journey to Normandy after this year.
But he said it was "essential" that commemoration continues into the future.
"With the Second World War if you take worldwide there were so many millions killed, we don't want that again and while people remember us and other comrades from the Second World War, with a bit of luck when they go round and see the rows and rows of graves it might make them stop and thing about fighting again, and that's the main aim."
As well as events in France, D-Day events will be held in the UK including in Portsmouth, one of the key places where tens of thousands of allied servicemen left for Normandy.