The D-Day landings marked the beginning of the end of World War Two, but at a huge cost in terms of the numbers of casualties.

"Soldiers, Sailors and Airmen of the Allied Expeditionary Force!

"You are about to embark upon the Great Crusade, toward which we have striven these many months. The eyes of the world are upon you. The hopes and prayers of liberty-loving people everywhere march with you.

"In company with our brave Allies and brothers-in-arms on other Fronts, you will bring about the destruction of the German war machine, the elimination of Nazi tyranny over the oppressed peoples of Europe, and security for ourselves in a free world.

"Your task will not be an easy one. Your enemy is well trained, well equipped and battle hardened. He will fight savagely.......

"I have full confidence in your devotion to duty and skill in battle. We will accept nothing less than full Victory!

Good Luck! And let us all beseech the blessing of Almighty God upon this great and noble undertaking."

Even as Dwight D Eisenhower’s message to the Allied Forces preparing to land on the beaches of Normandy on 6 June, 1944, was being read, the Allied commander himself was uncertain as to the chances of success of what was known as "Operation Overlord".

Winston Churchill, haunted by the memory of what had happened to troops landing at Gallipoli in the First World War in a dreadful and failed attack initiated by him, was equally fearful.

Yet the day of reckoning had arrived and there was no turning back. D-Day (the term itself does not mean anything other than a designated day for a military event - it was coined in the previous war) represented a last great gamble to re-establish an Allied presence on the European mainland, then occupied and dominated by Germany.

The plan was to penetrate the German defences at Normandy, thus relieving pressure on the Russians by drawing German forces west and make the last push into France and then on to Berlin.

American troops about to land on Omaha Beach

D-Day had been planned for the previous day - indeed ships were already in the English Channel - only to be delayed by an ominous weather forecast from the Sweeney family, who operated the weather forecasting station at Blacksod in Co Mayo.

By the early hours of 6 June, the weather had improved sufficiently to allow the invasion - one of the biggest in history - to advance.

Over 150,000 American, British and Canadian troops were under way in almost 7,000 ships, over 2,300 aircraft and 867 gliders.

They were preceded by 14,000 bombing raids over a period of months, and some 18,000 paratroopers getting in behind the lines.

Many of those crossing the lumpy waters of the channel that day had very limited military training.

Seasickness was rife, as many had never been on boats before. As dawn broke, a chaos of landing craft and ships, carrying everything from personnel to bicycles, jeeps, tanks, trucks, medical equipment and artillery had assembled in front of the five beaches of Normandy, codenamed Sword, Juno, Gold, Omaha and Utah.

Were the Germans surprised? Yes and no. The German High Command had generally believed the invasion would happen elsewhere.

At Calais, for example - the nearest French landing site to England. Others saw the Atlantic Wall - fortified by German forces - from the coast of Norway to the border with Spain - as adequate.

They had also been fooled by a highly sophisticated campaign of deception run by the Allies that involved months of false reporting of troop movements, disinformation and the use of double agents to spread deception.

Hitler had, reportedly, taken a sleeping tablet on the night of 5 June and issued orders not to be disturbed. By then he was relying on advice from mystics as much as his High Command.

Irwin Rommel, the so-called Desert Fox, had Normandy as a great threat but could not secure the forces he needed for his infantry on the French coast. Never the less, he was on leave in Germany for his wife’s birthday as the armada set sail.

Others saw the Atlantic Wall - fortified by German forces - from the coast of Norway to the border with Spain - as adequate.

As daylight broke, the Allies began their landing. Many German soldiers guarding the beaches were young, ill-trained or conscripted.

However, at Omaha Beach, a crack German coastal protection unit, rained artillery and sniper fire on American forces with deadly effect, as re-created in Steven Spielberg’s "Saving Private Ryan".

Other beaches had lighter opposition.

Ironically, many Allied troops never made it to the beaches. With 70lbs of kit, many were thrown or tumbled into several feet of water away from the beaches.

Hundreds drowned. Tank landing craft dug huge craters in the sand, causing craft behind them to dump tanks and their crews into deep holes in which they drowned.

The scene was described to us by Second Lieutenant, Michael d’Alton, from Dublin.

As Allied ships pounded German defences, the heavy gun emplacements responded. One gun on Omaha beach was repeatedly shelled but not before it had caused an estimated 10% of the casualties on that beach.

Pat Gillen, a young man who had run away from his home in Galway city, was a young commando and one of the first on Sword Beach.

Eight hours after the landings began an Allied spotter pilot over the beaches reported the sea to be running red with blood. Months later, bodies were still being washed ashore in France.

However, the advance had been made, but at great cost. There are no absolutely accurate figures for the casualties on D-Day but there are estimates for the Battle of Normandy, which continued for months. And the figures are dreadful - 320,000 Germans killed, missing and injured and over 200,000 Allied casualties.

Questions have been asked about the scale of the Allied bombing campaign that preceded Normandy to "soften up" German defences and which caused huge numbers of civilian deaths and injuries - at least 12,200 were killed. Eisenhower saw them as necessary collateral damage.

Within days, Operation Overlord had begun an irreversible penetration into Nazi-occupied Europe. Within weeks, despite many more horrific battles that followed, the road to Berlin was in sight and, with it, the beginning of the end of World War Two.But a terrible final price would be paid - on both sides.