THE foundations for the Allied invasion of occupied Europe lay, ironically, in one of their worst defeats of the war.

In allowing the Wehrmacht to halt outside Dunkirk at the end of May 1940, Hitler lost the chance to annihilate 338,000 allied troops and put Britain out of the war for good.

The famous evacuation was one of the main foundations upon which the Allied invasion of Europe was built, enabling Britain to continue to wage war against Nazi Germany.

Churchill and his countrymen fought on virtually alone until December 1941, when Japanese bombers almost destroyed the US naval fleet at Pearl Harbour in Hawaii.

Soon after that day America and Britain agreed to pool their military and economic resources under combined chiefs of staff, agreeing that the destruction of the Nazi war machine should take priority over the Japanese.

By May 1943 the Allies had secured some notable victories, having shored up the Far East and Mediterranean theatres – and importantly wrested control of the sea from the deadly German U-boats.

The blueprint for D-Day came in August 1943 during a conference between Churchill and Roosevelt in Quebec, Canada.

Surrounded by military advisers, the pair agreed on an invasion through Northern France to take place in May 1944.

Planners then began a series of detailed preparations conducted under the strictest secrecy, codenamed Operation Overlord.

Key to its success would be fooling the Germans into thinking the landings would take place at Calais.

This would enable the actual attack to take place at the next best location on the French coast – the Normandy beaches.

The decisive phase of Overlord involved four key elements – an aerial bombardment of the French coast, an airborne assault to secure key targets, a further naval bombardment of shore placements followed by infantry landings.

Large parts of the south coast were sealed off as thousands of acres of land were annexed for military training and storage.

A crucial break in the weather allowed the invasion to begin on Tuesday, June 6.

Eisenhower had a final conference with his commanders before announcing: “OK, let’s go.”

Within two hours of that decision, all the Allied vessels – ranging from Falmouth in the west to Newhaven in the east – started heading out to sea.

Although the thousands of infantry soldiers onboard were the first to leave English shores, the first Allied soldiers to physically engage the enemy were the airborne troops parachuted into Normandy shortly after midnight.

Many of them left from Tarrant Rushton at 11pm in C57 transport planes and huge gliders containing jeeps, mobile guns and tanks.

Civilians in Weymouth and Dorchester were directly under the flight path and those watching witnessed the greatest mass movement of aircraft that has ever taken place.

A British unit that flew from Tarrant Rushton was the first to go into action on D–Day.

Major John Howard's D Company of the Ox and Bucks landed next to the Orne canal shortly after midnight on June 6.

Within 20 minutes they had secured the newly-christened Pegasus Bridge across the waterway – the first area of France to fall and be recaptured by the Allies.

By 3am on June 6 the warships were in position off the beaches, in clear sight of the German positions. It was the 40,000 men who sailed from Weymouth and Portland who bore the brunt of the German defences.

German soldiers on the shore watched as landing craft raced towards them, under orders not to start firing until the landing craft started unloading.

As they did so the Americans inside were greeted by a hail of machinegun fire and shells.

Allied unloading stopped at around 10pm on D-Day.

By then 175,000 men had been delivered into Normandy, of whom 4,900 were dead or seriously injured. An invasion front more than 60 miles long and six miles deep in places had been established.

In one day the Allied forces had breached a defensive structure that took the German Army four years to build.

The world’s largest amphibious invasion force had gained a foothold, thanks to the world"s biggest deception.

Having been fooled into thinking the Allies would land at Calais, the German Army had been largely unaware until the last minute of the armada heading towards Normandy.

Once commanders on the ground knew what was happening, the only man who could set the defensive wheels in motion – Hitler – was asleep in Berlin and could not be woken.

This delay in decision making gave the Allies valuable time to pour more men and equipment into Normandy before any serious counter attack was made.