1. D-Day was supposed to happen a day earlier
The original date for D-Day was set to be 5 June 1944.
The landings had been planned with very specific weather and tides conditions in mind, but as the day approached, the weather got worse and unpredictable. High winds and torrential rain meant the operation had to be delayed.
Even on 6 June 1944 the weather was far from perfect, but it was still good enough for the troops to invade the shores of Normandy.
A further postponement would have meant waiting at least two more weeks as the phase of the moon and tides would have changed.
2. 'H-Hour' is when the operation was set to begin
'H-Hour' was the term used to indicate the time on 6 June when the military operation was set to begin.
For D-Day, it was set to 06:30 in the morning – the time when the attacks on the beaches began.
At that time, US troops landed at Utah and Omaha beaches, the British arrived at Gold and Sword beaches and the Canadians landed at Juno beach.
3. Normandy was seen as an unlikely point for an attack
An attack from the sea was not foreseen by the Germans.
In order to succeed in a military invasion of Normandy, the attacking forces needed to not only make it successfully on to the beaches with their military equipment, but they needed to either carry their military and food supplies with them or have them shipped over.
This is why Calais was the location Germans believed an attack could take place: the distance from England was shorter than that between the UK and Normandy, and there was a large, active port.
4. Germans expected an attack on Norway
A game of deception code-named 'Bodyguard' was put into action by the Allies.
Operation Fortitude built up to the 1944 Normandy landings. Divided into the North and South sub-plans of deception, it aimed to mislead the German high commands as to where an invasion would take place.
Phantom field armies, made up of inflatable vehicles and submarines, were placed in strategic locations to simulate threats on Norway (Fortitude North) and Pas de Calais (Fortitude South).
Thanks to Operation Fortitude, German reinforcements were delayed to reach Normandy when the attack finally took place.
5. D-Day was the largest single-day amphibious invasion in history
Planning for Operation Neptune took months and it began in 1943.
It involved 6,939 vessels and 4,126 landing craft which assembled on 5 June 1944 off the Isle of Wight.
The landings on the shores of Normandy were preceded by an airborne assault to the German troops stationed in France and naval bombardments.
The 80km stretch of coast was divided into five sectors: Utah, Omaha, Gold, Juno, and Sword.
Watch: D-Day veterans recall their experiences.
6. Spies helped with the success of D-Day operations
Despite the German occupation of France, resistance groups were still active and spies and saboteurs of the Nazi regime kept close contacts with the Allies.
The Special Operations Executive was set up in 1940 to help resistance movements in Germany-occupied territories thrive despite the occupation.
Informants in France provided the Allies with intelligence on German defences and carried out acts of sabotage to disrupt the German war effort.
Many of the resistance activities revolved around the rail network in France ahead of D-Day. Saboteurs deliberately damaged railways around Normandy and slowed down transport services as well as industrial military factory production.
Those acts were non-violent but helped greatly.
7. Brits could not travel to Ireland in the lead up to D-Day
All travel to Ireland was barred from 12 March 1944. Ireland was one of the neutral countries during the Second World War.
Even though Ireland never blocked Allied forces aircraft from using the Donegal Corridor, and even though Irish and Allied intelligence tacitly co-operated during the war, it was decided to stop all travel to Ireland ahead of D-Day.
This decision was taken to prevent information concerning the date of D-Day to be leaked.
8. The Luftwaffe was greatly outnumbered
The German Air Force, known as the Luftwaffe, was outnumbered 30:1 on D-Day.
Because of the highly strategic nature of the D-Day operations, the German Navy and the German Air Force had little means to resist the invasion.
The Luftwaffe had withdrawn nearly all its fighters to counter American daylight bombing operations over Germany so there were very few aircraft left in France.
9. D-Day came at a price
While D-Day marked the beginning of the liberation of Western Europe from Nazi control during the Second World War, it came at an enormous price in terms of lives lost in the battle.
There are currently 27 war cemeteries in Normandy and they contain the remains of hundreds of thousands of people who lost their lives on and after D-Day.
From the records of the war cemeteries in Normandy, it is estimated that in a very short span of time more than 110,000 people lost their lives. They were:
- 77,866 German
- 17,769 British
- 9,386 American
- 5,002 Canadian
- 650 Poles
10. Anne Frank learned about D-Day from the BBC
Anne Frank's diary is probably one of the most compelling, heartbreaking personal records of Jewish people who were hiding during the Second World War and hoping for the conflict to end.
She kept a diary from 12 June 1942 until the day she and her family were captured on 1 August 1944.
An entry dated 6 June 1944 reveals that Anne recorded hearing the news of D-Day from the BBC at 12pm.
"Is this really the beginning of the long-awaited liberation?" she wrote in her diary.
"We don't know yet. But where there's hope, there's life.
"It fills us with fresh courage and makes us strong again."
Cover image: Royal Marines land at Normandy in June 1944 (Picture: PA).