Training for the invasion was intense and meticulous in every aspect. For the assault upon the Merville Battery, for example, an exact replica of the battle ground was constructed for the 9th Battalion to train on. This model, as well as featuring every known aspect of the Battery defences, also replicated every hedge and fence that lay between the Battery and the Rendezvous Point on DZ-V. Despite this activity and the precise nature of their training, none but the most senior officers in the 6th Airborne Division had any idea what or where their objectives were.
It was intended that D-Day should be attempted during May 1944, but delays in the production of landing craft had led to a postponement until June. On the 25th May 1944, the various elements of the 6th Airborne Division moved into their concentration areas around the aerodromes of 38 and 46 Groups, from where they were to take-off for Normandy. These camps were surrounded by barbed wire fencing and armed guards, and once in, no one, save those with special permission, was allowed out or could have any communication whatsoever with the outside world. This isolation naturally caused a degree of frustration, but it was a credit to the Division that there was not a single reported case of disobedience.
It was in these concentration areas, on the 30th May, that all ranks of the Division learned of the precise nature of their allotted role. Maps, aerial photographs and accurate scale models of their objectives were provided in order that the men should know every aspect of their role in the forthcoming battle. In deference to the unfortunately common occurrence that an airborne soldier could potentially be dropped miles from his intended drop zone, an effort was made to make every man fully aware of all tasks that the Division was to undertake, so that he should be completely familiar with his surroundings should he land astray. In these final days before D-Day that the plan was honed. Men continued to prepare themselves for what lay ahead, discussing all manner of potential difficulties and the necessary methods to overcome them.
D-Day was scheduled to take place at dawn on the 5th June, with the paratroopers taking to the air on the previous evening, however bad weather resulted in the invasion being postponed for twenty-four hours. The weather had been perfect in May, but now that the Allies were at last ready, the worst storm for years broke out over the English Channel. Good weather was essential for a successful attack, not just for the troops at sea, but also for those in the air. High winds would account for many casualties amongst the paratroopers before a shot was fired, whilst the gliders would be at a greater risk of their tow ropes breaking before they reached the landing zone.
The invasion had to take place some time between the 5th and 7th June, because it was a period that favoured the airborne troops with a late-rising full Moon and also gave the correct tide conditions for a sea-borne assault. The tide at the time was high enough for the troops to be landed as close to the German defences as possible, but also low enough to reveal many of the underwater mines and obstructions that had been laid. The next period when this same tide would be available was the 19th June, but to attack then would mean the paratroopers jumping in total darkness. To further complicate matters, the invasion fleet was already at sea and it did not have enough fuel to wait until the 7th June. If the attack was not launched on the 6th June, it would mean the postponement of Operation Overlord until July. General Eisenhower, out of regard for the morale of the men under his command and also keeping the invasion of Normandy a secret, regarded such a delay as "too bitter to contemplate."
In the closing hours for the 4th June, however, Eisenhower was informed by his meteorological staff that there would be a gradual improvement of conditions during the day which would continue through the morning of the 6th June, after which the weather would again deteriorate. The Allies had only previously launched an invasion in ideal weather, but the conditions available for Normandy were far below what was the accepted minimum requirement. Eisenhower, after consultation with his Generals, thought silently for several minutes before declaring, "I am quite positive we must give the order. I don't like it, but there it is. I don't see how we can do anything else." Operation Overlord was on.
The order to proceed was circulated. To many of the soldiers waiting with the invasion fleet in the English Channel, having struggled with terrible sea sickness for three days, the order, to go anywhere but stay on a boat for another moment, came as something of a relief. Back in England, the Airborne troops made their final preparations, and for the first time their RAF crews were briefed.