None of the men of the 1st Battalion of the Royal Hampshires was surprised that the fight would be tough. As they doggedly advanced up 'Gold' beach on D-Day, every man knew that surviving the murderous criss-cross of machine-gun fire would demand a miracle.
The village of Le Hamel, although no more than a few hundred yards beyond the surf, never seemed to get any closer. The bullets mercilessly cut down their commanding officer as well as several middle-ranking officers, and as the day wore on, it looked as if the entire battalion would be slaughtered on the beach.
Fortunately, the arrival of the 2nd Devons helped turn the tide. The combined force managed to overwhelm the Germans at Le Hamel, and soon the attention of the British turned to the small town of Arromanches. On this sector of Gold, at least, it finally looked as if D-Day might be a success.
At around 4pm, the Germans responded with an artillery barrage, causing the troops to duck down inside the recently captured German fortifications. Nothing, the British thought, could penetrate the defences that thousands of slave labourers had built over the past four years.
But within minutes of the first shells raining down, something strange happened. A slightly fruity odour hung in the air. Many of the men soon began to tremble and sweat - in itself nothing unusual during such a relentless barrage - but most also found that their eyes were extremely itchy.
When the soldiers started looking at each in anxious bewilderment, some noticed that their pupils were also excessively small.
A minute or two later, noses started running, and mouths frothed with seemingly endless quantities of saliva. Soon, the troops had trouble breathing; many went into convulsions. Bowels and bladders became uncontrollable, and heart rates slowed to near standstills.
Unconsciousness overcame all but a few, and within 15 minutes of the start of the barrage, 967 members of the two battalions lay dead. By 5pm, a further 312 had died, leaving as the only survivors those who had been wounded on the beach, and the medics who were tending them.
All along the Normandy beaches that day, tens of thousands of Allied troops met the same horrific fate - all poisoned by a nerve agent called Ethyl dimethylphosphoramidocyanidate - or, to give it its more punchy German name, Tabun.
At least, that's how it might have been . . .
Thankfully, this chilling scenario never came to pass. As we all know, DDay did not fail and the Allies went on to defeat Hitler. But if it had not succeeded, their only hope of seeing off the Germans would have been to fall back on the scientists who were working in New Mexico to develop a secret and unproven device, the atomic bomb.
All this leads one to ask the question that has vexed historians since 1945: why didn't Hitler use chemical weapons against the Allies? After all, he had shown no qualms against using gas on Jewish men, women and children, so why not against enemy troops as well?
Until now, many believed his reluctance to use these weapons on Allied soldiers stemmed from his own bitter experiences of being gassed during World War I.
As a young soldier, on the night of October 13-14, 1918, near Ypres, Corporal Hitler was exposed to mustard gas released by the British that left him temporarily blind. It ended his war, and apparently left him with a strong desire never to see gas used again.
But now a startling new explanation has come to light. According to Frank J. Dinan, a distinguished professor of chemistry and biochemistry at Canisius College in Buffalo, New York State, a scientist close to Hitler exaggerated the Allies' capability of hitting back with their own chemical weapons, which caused the Fuhrer to rethink his plans.
If Professor Dinan's extraordinary claim is true, it means that a German scientist, up until now regarded as a war criminal, might be one of the greatest unsung heroes of the 20th century.
That man was Otto Ambros. Born in 1901, he was a highly able chemist who earned his doctorate at Munich University in 1925. He initially worked for the German chemical company BASF, but by 1938 had risen to become a board member of the giant IG Farben, where he helped mastermind the firm's chemical weapons section.
Industrious and charismatic, Ambros was highly regarded by the Nazis, and he was given the use of concentration camp prisoners at Buna-Werk IV, a subsidiary of Auschwitz, to help produce his chemical weaponry.
Although Ambros later claimed that he had worried dreadfully about the conditions in which the prisoners worked, there can be little doubt that such sympathy was not overtly expressed during the war.
As Ambros himself was to write to an IG Farben director in April 1941: 'On the occasion of a dinner given for us by the management of the concentration camp, we furthermore determined all the arrangements relating to the involvement of the really excellent concentration-camp operation.'
Ambros's hard work earned him much prestige as well as the War Merit Cross, and the 1st and 2nd Class and the Knight's Cross of the War Merit Cross. Designated as a 'military economy leader', Ambros was considered essential to the war effort, and he soon mixed with the elite of the Third Reich.
One of the chemicals on which Ambros invested most time and energy was Tabun. It was first manufactured on December 23, 1936, when Dr Gerhard Schrader of IG Farben was preparing compounds he could use as insecticides.
Schrader discovered that Tabun was extremely effective against leaf lice, but it was not until the following month that its toxicity towards humans was established.
In fact, it was Schrader himself who, along with a laboratory assistant, were the first to suffer Tabun's effects. While working on the chemical, they were exposed to its fumes, and rapidly found themselves short of breath. After swiftly seeking fresh air, the two men recovered, but they were extremely lucky.
Tabun was quickly identified as one of the earliest nerve agents, which are deadly to many mammals because they destroy the functioning of the nervous system.
Once Tabun is absorbed, it prevents the action of a key enzyme that regulates all nerve transmission processes. Victims suffer blindness, lose control of bodily functions and suffocate. Death follows in a matter of minutes.
But Tabun is particularly dangerous as it can be absorbed through the lungs, the skin and even the eyes. Even one millilitre absorbed through the skin can be fatal.
It was hardly surprising that the Nazis quickly identified Tabun as being a promising new weapon. Indeed, they even kept it secret for fear the Allies would also be able to manufacture it.
After more tests and investigations, it was decided to develop a plant to produce the poison on an industrial scale. Progress was slow as the work was complicated and dangerous. Despite extreme precautions by the 3,000-stong workforce, more than 300 accidents took place, and ten workers suffered horrific deaths when Tabun was accidentally spilled.
Nevertheless, by mid-1943, the Germans had managed to manufacture 12,500 tons of Tabun, much of which was loaded into munitions such as shells and bombs. At the time, the Nazis had without doubt the deadliest weapon of the war.
In May that year, a meeting took place at Hitler's Wolf 's Lair headquarters in East Prussia that would have far-reaching ramifications for the whole of history. The Germans had just been defeated at Stalingrad, and Hitler had summoned both armaments minister Albert Speer and Otto Ambros to discuss the use of chemical weapons.
Many senior Nazis had been imploring Hitler to use Tabun against the Russians, but he had refused, partly because he feared the Allies also had access to similar weapons.
Hitler asked Ambros whether his fears were justified. Ambros told the Fuhrer the Allies would be able to produce vast quantities of mustard gas, but this didn't bother Hitler.
He wanted to know if the British and Americans also had access to much deadlier nerve agents, such as Tabun.
'I understand that the countries with petroleum are in a position to make more mustard gas,' Hitler said, 'but Germany has a special gas, Tabun. In this we have a monopoly in Germany.'
Hitler then enquired whether the Allies could make Tabun and a similar nerve agent, Sarin.
And it was at this point that Ambros made the claim that Professor Dinan believes may well have changed the course of the war.
'I have justified reasons to assume that Tabun, too, is known abroad,' he said. 'I know that Tabun was publicised as early as 1902, that Sarin was patented, and that these substances appeared in patents.'
It was an extraordinary answer, as it was completely untrue. And he knew it. What's more, Professor Dinan argues that it was when Hitler realised that the Allies might be able to retaliate with Tabun or similar chemicals that he expressed deep disappointment and abandoned the meeting.
For the rest of the war, many in Hitler's entourage continued to press him to use nerve agents such as Tabun.
In the autumn of 1944, for example, Robert Ley, the head of the German Labour Front, implored Albert Speer to convince Hitler of the merits of nerve gases. 'He must use it!' he pleaded. 'Now he has to do it! When else! This is the last moment!'
The appeals fell on stony ground, however, and Hitler never changed his mind. But the fundamental question remains. Why did Ambros mislead Hitler, and did he do so deliberately?
Professor Dinan and other experts have made extensive searches of the scientific literature between 1896 and 1911 to see whether, as Ambros suggested, Tabun had indeed been mentioned in 1902. So far, nothing has been found, which shows Ambros was certainly misleading his leader.
But was he doing so deliberately? Well, it is extremely unlikely that Ambros was simply mistaken. He was one of the most renowned chemists in Germany, if not the world, and there was little about chemical weaponry that he did not know. As a senior figure in IG Farben, he had access to all the relevant scientific information, and it seems implausible that he could have confused 1937 - the year of Tabun's actual patent - with its supposed publicity in 1902.
Instead, Professor Dinan's startling conclusion is that Ambros was quite possibly lying to save the lives of millions. As a man who had spent most of his life working for the Nazis and using slave labour, it appears uncharacteristic that Ambros would suddenly have an attack of conscience - but it cannot be ruled out.
Ambros, more than anyone else in that room in May 1943, was able to envisage the devastating consequences of both sides launching a chemical war.
And if this really was the case, then Ambros was a truly extraordinary figure, around which the future of the war pivoted. For that small lie would appear to have changed the course not only of the war, but of the whole of human history.
Of course, it is also conceivable that the meeting between Hitler and Ambros never actually took place. The chemist recounted details of the conversation during his trial for crimes against humanity at Nuremberg from August 1947 to July 1948.
Casting himself as a white knight may have been an attempt to curry favour with the court - in the end, he was sentenced to eight years. Twenty years after his death in 1990, we may never know.
What is certain, however, is that if Professor Dinan is right, then Otto Ambros is that rarest of breeds - a war criminal and a hero.