It was three minutes past two on the morning of 28 April 1944. A flotilla of American warships was approaching Slapton Sands on the Devon coast in south-west England, a crucial practice exercise in advance of the D-Day landings. Exercise Tiger was a 300-vessel, 30,000-men dress rehearsal for the biggest amphibious landing in history. It would enable Allied commanders to fine-tune their Normandy battle plan.

Angelo Crapanzano was one of those involved in the operation. He was in the engine room of his vessel, named LST 507, when it was suddenly rocked by a tremendous explosion. ‘I got this sensation of flying up, back, and when I came down I must have bumped my head someplace and must have been out for a few seconds, because I felt cold on my legs,’ he later recalled.

As he recovered consciousness, he realised that the ship must have been hit by a torpedo. This was indeed the case. A German naval squadron had encountered the Allied flotilla by chance and immediately opened fire.

‘The ship was burning,’ said Crapanzano. ‘[It] was split in half . . .fire went from the bow all the way back to the wheelhouse.’ The sea also was on fire, because the fuel tanks had ruptured and poured oil into the water.

Torcross Memorial

LST 507 was not the only ship to be hit. Crapanzano witnessed a second landing vessel, LST 531, coming under attack. She sank in ten minutes, killing almost everyone on board. A third ship also burst into flames, another victim of the German ambush.

By about 2.20 a.m., the captain of Crapanzano’s vessel realized that she was fatally damaged. ‘The tank deck was burning fiercely. It [was] just like a gas jet stove. And all the heat going up to the top deck.’

The order was given to abandon ship. Crapanzano braced himself for the forty-foot jump into the sea, hitting the water at high speed and plunging deep beneath the surface. ‘It was frigid. It was like unbelievable, unbelievable cold.’ But he didn’t think of the chill for long. He was too busy trying to escape the burning fuel on the water’s surface.

Of the twelve life rafts on the LST, only one had been lowered into the water. It was completely burned, but Crapanzano and ten others managed to cling to it. They desperately kicked themselves away from the ship so as not to get sucked under when it sank.

Crapanzano witnessed scenes that would haunt him for years. ‘I saw bodies with arms off, heads off, heads split open, you wouldn’t believe what the hell goes on.’

Nine German E-boats had attacked the Allied fleet as it headed for Slapton Sands. Their assault had come hard and fast. Three LSTs were totally crippled and a fourth was badly damaged by friendly fire. The E-boats had got away before the Allies could return fire.

A staggering 638 servicemen were killed in a matter of minutes and many more were flailing around in the burning water, desperately hoping to be rescued. But there was to be no help for Crapanzano and his comrades. The practice landing operation was set to continue, despite the German attack, and the remaining ships pressed on at full speed towards Slapton Sands, leaving the dead and dying in the water.

The beach landings were to prove the setting for the day’s second tragedy. General Eisenhower, the Supreme Allied Commander, had ordered that real ammunition be used, in order that men could experience actual battlefield conditions. It was a disastrous decision, one rendered even more dangerous by the fact that the entire exercise was mistimed. The British cruiser HMS Hawkins was still shelling the beach as the soldiers stormed ashore, killing a further 308 men. The landings rapidly turned into a bloodbath.

At the same time that men were coming ashore under heavy friendly fire, Angelo Crapanzano was still struggling to keep alive in the icy water. He was acutely aware of the dangers of hypothermia and tried to keep up the spirits of the ten men clinging to the raft.

‘I kept saying to them: “Don’t fall asleep, whatever you do. If you fall asleep you’re dead.”’

But one by one they slipped into unconsciousness and were swallowed by the sea. Soon there was no one left alive except for Crapanzano and one of his comrades.

They’d been in the water for four-and-a-half hours when Crapanzano noticed a faint light. ‘I see this light, going up and down, and it seems to be getting bigger. I immediately assume that help is coming.’

The memorial erected at Utah Beach, Normandy

Help was indeed at hand. The light came from LST 515, one of the ships that had belatedly put back to sea in order to search for survivors. The crewmen were scanning the water when they spotted

Crapanzano’s head. At first they thought it was yet another corpse, but then one of them noticed it move. Crapanzano was still alive.

He was plucked from the sea, wrapped in blankets and eventually transferred to a Dorset hospital where he made a full recovery. It was several days before he learned the full extent of the Slapton Sands disaster. Exercise Tiger had cost the lives of 946 American servicemen.

Everyone involved in the operation was sworn to secrecy. It was vital that the Germans knew nothing of the practice landing. The massive loss of life was also highly embarrassing for the Allied high command, who wanted to keep it firmly under wraps.

And so it remained for many years, an episode of the war that was deliberately expunged from the records. Not until four decades later, in 1984, was a memorial finally erected to the memory of the men who lost their lives in the practice landings for D-Day.

This excerpt is from Fascinating Footnotes From History by Giles Milton, published by John Murray.