One image still brings tears to his eyes. A young American had run from his landing craft and sought cover behind a concrete block. Severloh, then a young lance-corporal in the German army in Normandy, aimed his rifle at the GI. He fired and hit the enemy square in the forehead. The American’s helmet flew away and rolled into the sea, his chin sank to his chest and he collapsed dead on the beach.
Tormented by the memory, Severloh now weeps at the thought of the unknown soldier’s death.
Severloh was safe in an almost impregnable concrete bunker overlooking the beach. He had an unimpeded view of the oncoming Allied forces. He was the last German soldier firing, and may have accounted for about 3,000 American casualties, almost three-quarters of all the US losses at Omaha. The Americans came to know him as the Beast of Omaha.
He had been saved from the waves of Allied bombing by the poor weather. The US aircrews were worried that if they allowed their bombs to fall too soon they might destroy their own landing ships. As they flew over they lingered before releasing their weapons, meaning the bombs often landed far behind the Nazi bunkers.
The Germans joked that the ‘Amis’ - their slang for the US forces - had merely bombed French cows and farmers rather than the German installations.
Alerted by the bombers, Severloh and the 29 others in his bunker rushed to their firing holes and prepared for the onslaught. Severloh, then just 20, gasped when he saw the ocean. He was confronted by what seemed to be a wall of Allied ships. He said: "My God. How am I going to get out of this mess?"
The veteran explained: "What could I do? I just thought that I was never going to make it to the rear. I thought that I was going to shoot for my very life. It was them or me - that is what I thought."
As the landing ships neared the beach, Severloh listened to the final orders from his commander, Lieutenant Berhard Frerking. They wanted to stop the Americans while they were still in the water and could not move easily. But if he fired too soon - while the soldiers were still some way out in the water - he risked missing them.
Frerking explained: "You must open fire when the enemy is knee-deep in the water and is still unable to run quickly."
Severloh had seen little action before. His previous stint on the Eastern Front had been cut short by tonsillitis. But he was anything but enthusiastic. Severloh said: "I never wanted to be in the war. I never wanted to be in France. I never wanted to be in that bunker firing a machine gun.
"I saw how the water sprayed up where my machine gun bursts landed, and when the small fountains came closer to the GIs, they threw themselves down. Very soon the first bodies were drifting in the waves of the rising tide. In a short time, all the Americans down there were shot."
He fired for nine hours, using up all the 12,000 machine-gun rounds. The sea turned red with the blood from the bodies. When he had no more bullets for the machine-gun, he started firing on the US soldiers with his rifle, firing off another 400 rifle rounds at the terrified GIs.
A leading German historical expert of the Second World War, Helmut Konrad Freiherr von Keusgen, believes Severloh may have accounted for 3,000 of the 4,200 American casualties on the day.
Severloh is less sure about the number, but said: "It was definitely at least 1,000 men, most likely more than 2,000. But I do not know how many men I shot. It was awful. Thinking about it makes me want to throw up. I almost emptied an entire infantry landing craft. The sea was red around it and I could hear an American officer shouting hysterically in a loudspeaker."
Lt-col Stuart Crawford, formerly of the Royal Tank Regiment, and a defence consultant, said it was entirely possible that a single German soldier had killed so many GIs.
He said: "I have fired that machine-gun. I did it as part of my training, and it has an extremely high rate of fire. He was in a position which was almost impervious to the weapons which the Americans could bring to bear on him. The Americans made the mistake of not landing tanks with the first wave of troops, so they had no support or protection."