Ted Cordery was a 20-year-old torpedo man for the navy when he stood on the upper deck of HMS Belfast and looked helplessly on as dozens of men drowned around him.
D-Day, on June 6 1944, was the world's largest seaborne assault and the beginning of the Allied invasion of Nazi-occupied Europe.
But many of the first troops to arrive at Normandy, in northern France, were accidentally dropped off by their landing boats in too-deep water, where they sank under the weight of their guns and equipment.
Others suffered from seasickness caused by the flat bottoms on the smaller boats "bouncing" across the waves.
Speaking to the BBC from his home in Oxford, Ted, now 95, vividly remembers the events of that day 75 years ago and says the horrific things he witnessed will stay with him forever.
He says: "I felt so sorry for the men. They were coming from a fair way out to get to the beach, and they were all in their uniforms and carrying guns and their own food, so they all had these cans weighing them down.
"I looked at them as we were passing them and I thought to myself, if you're seasick and you're then expected to get off the boat and start fighting… come on.
"The water was a bit choppy, which made no difference to us, but if you're in a flat bottom boat and its a bit choppy you can really feel it.
"What those men went through. It's asking a lot isn't it? I think so. Those men are bloody marvellous.
"So many of them didn't make it because they were dropped too far from the land. They went straight in the deep water and drowned."
D-Day began with a damp, grey dawn over the English Channel. More than 6,330 boats carrying thousands of men readied themselves to launch the invasion of Nazi-occupied Europe.
The night before, Ted and his fellow crew were told they were joining a large operation, but they had no idea of the scale until they saw the other ships.
But they were not nervous. Ted says: "Well, you see, once you've gone to sea you've always got to be ready for action, U-boats, anything.
"It's like everything, you go into something strange and of course you're apprehensive, even if you're not frightened, because you just get on with it - and please God you'll be alright."
HMS Belfast was the flagship of Bombardment Force E, supporting troops landing at Gold and Juno beaches by attacking German defences.
The ship came under occasional fire from German artillery and dive-bombers but managed to battle on unscathed as it continued to hit German positions.
Working predominantly on the upper deck, Ted had a bird's eye view of the action unfolding around him.
He says: "When we got near the coast we could see all the activity and we just went in and anchored up and as soon as we got there, more or less, we opened fire."
As one of the larger warships present on D-Day, HMS Belfast also had a fully equipped sick bay staffed by surgeons and took hundreds of casualties on board during the first day of fighting.
After destroying the German defence batteries, the crew was tasked with clearing the beach and bringing wounded soldiers back to the ship to receive medical treatment.
Ted was trained to operate one of Belfast's two cranes, which allowed him to lift stretchers up on to the deck.
156,000allied troops landed in Normandy, across
7,000ships and landing craft involved and 10,000 vehicles
4,400from the combined allied forces died on the day
4,000 - 9,000German casualties
Thousandsof French civilians also died
It was a difficult job, made harder when he realised how badly injured the troops were.
Ted says: "I'll die with this memory. These men were wounded. We put them on the stretcher. You'd then put them on a cart and get them down the beach and then put them on a pontoon on the beach.
"And then they would be taken out to the boat. And I'd lift those men out... and the injuries I saw, I couldn't tell you."
Fighting back tears, he adds: "There was nothing I could do about it. I looked down at them, and I cried.
"I'm a soft sod. You would never believe what they went through. Those poor men.
"They took them to the sick bay, and if 2% or 3% of them survived I'd be surprised.
"They did what they could for them, but they were too far gone - they were mostly dead before they got them in the sick bay.
"But the injuries - faces, stomachs, legs off - oh God. I know nurses would say to me 'silly sod', they see it every day, in a more clinical fashion.
"But the way I saw it - God, I think to myself, I'm lucky to be alive. Those poor people.
"I think there were about 10,000 men lost that day. And what for? We don't learn do we?"
Apart from periods replenishing ammunition, HMS Belfast was almost continuously in action over the five weeks after D-Day and fired thousands of rounds from her guns in support of Allied troops fighting their way inland.
But D-Day was not the only battle Ted fought in during his time onboard HMS Belfast.
Between 1943 and 1944, he took part in some of the navy's most intense and dangerous operations including the Arctic Convoys and the Battle of North Cape.
Immediately after the war ended Ted continued his military service as a minesweeper, working off the coast of Scotland.
He left the navy in 1946 and returned to his job as an apprentice printer where he went on to "work at practically every paper on Fleet Street".
Just one month after D-Day Ted met a woman named Lila while he was on leave and married her three weeks later in August 1944.
They had one son, two grandchildren and two great-grandchildren and were together until her death in 1991.
Ten years later Ted met and married his second wife, Glynis, with whom he lives in Oxford's suburbs.
They will attend the 75th anniversary events in Normandy this week.
Many assumed that technological advances would ensure the World War Two was less horrific than the Great War.
But the fighting during the Battle of Normandy, which followed D-Day, was as bloody as it had been in the trenches of the World War One..
Casualty rates were slightly higher than they were during a typical day during the Battle of the Somme in 1916.
Ted says: "I well up every time I talk about it. Sometimes I think about it when I'm lying in bed awake.
"I don't like to dwell upon it too much because there's nothing you can do about it. But like millions of others I did my bit."