DELIVERANCE? Debarkation? Destiny? Decision? Determination? Dooms? What does the D in D-Day stand for?

Well, nothing really.

Unlike most of the other code names deployed 80 years ago, the main one by which we know the operation doesn’t mean anything more than 'day'. It's 'Day-Day'.

The whole project was known as Operation Overlord, a grand Churchillian name for the largest seaborne invasion of all time. The naval part of Overlord was codenamed Neptune, after the Roman god of the sea.

The US build-up of troops was known as Operation Bolero because, like the Latin music, it was going to have a slow but deliberate pace and grow to a crashing climax.

There was a big propaganda operation, known as Operation Bodyguard, to convince the Germans that the invasion was going to come via Calais with a secondary attack on Norway.

Operation Bodyguard involved the creation of phantom armies complete with inflatable tanks and fake landing craft, supplied by Shepperton film studios' set designers, in Kent, and it got its name after Winston Churchill told Joseph Stalin: “In wartime, truth is so precious that she should always be attended by a bodyguard of lies.”

Bodyguard even involved a visit to Gibraltar by a lookalike of General Bernard Montgomery, the British commander, intended to suggest a Mediterranean landing was in the offing.

One of the few code names that was meaningless was 'mulberry', which was the name given to the portable prefabricated harbours which were towed across the Channel at eight miles an hour and placed at Gold and Omaha beaches. Their development had begun in the summer of 1943 when they were referred to as the 'artificial harbours', but it was soon realised that this was a security risk so a list of random words was consulted. Top of the list was 'mulberry', and so the harbours were code named.

Other words on the list were used to generate code names for parts of the harbours: the blockships on which they were to be anchored were called 'corncobs', the outer breakwaters were 'gooseberries', the caissons were 'phoenixes', the roadways were known as 'whales' and 'beetles', and the pierheads were 'spuds'.

No one knew precisely when the invasion would go ahead so they didn’t know the date by which the mulberries would be required to be in place, but they began to work out what supplies would need to be delivered over them in the days after the invasion to ensure the soldiers could fight ahead. The first day after the landing was known as D+1, the second was D+2...

So the day itself became D-Day – but no one knew when it was going to be.

For D-Day to be successful it needed a full moon to shed light on proceedings and to ensure a high tide. June 5 was pencilled in, but as it approached, the weather worsened, with depression after depression scudding across the Atlantic to batter northern Europe. D-Day was going to be postponed for a fortnight until June 18-20, the next suitable D-Days.

But on the evening of June 4, weatherman Group Captain James Stagg saw that a weather window was about to open. An unseasonal cold front had accelerated as it crossed the Atlantic and was due to hit on June 5. The weather was so bad that day that the German commander in Normandy, Erwin Rommel, thought no invasion was possible so returned to Germany with a pair of shoes as a 50th birthday present for his wife.

But Stagg had noticed the wet front behind the cold front was beginning to slow down, creating a gap that was increasing from 24 hours towards 48.

At a 4am briefing on June 5, Stagg, a 29-year-old Scot who had been given the temporary rank of group captain, told the supreme commander Dwight D Eisenhower – not without misgivings – that the next day would see a break in the skies. Eisenhower said go... and D-Day became June 6.

So really, it was a weatherman who set the date for D-Day.

On Tuesday, June 6, 1944, Operation Neptune began, the mulberries were towed into place, and Operation Bodyguard had thrown the Germans off the scent of Operation Overlord – they knew something was coming, but thought it would be called Operation Overlock, and rather than throw all their resources at stopping the Normandy landings, they held back, convinced by the propaganda that this was just a diversion and the main invasion would come elsewhere along the French coast.

They were wrong, and the British weatherman was doubly right. Not only did his window open wide enough for the landings to begin successfully but a major storm hit Normandy on June 19, which would have been D-Day had D-Day been postponed from early June. It was so strong it would have prevented any beach landings.