In 1943 the British and Americans plan the opening of a 'Second Front' in Northwest Europe. Huge numbers of troops, aircraft and ships begin to assemble in England for the invasion of France. They train relentlessly for what will prove the largest amphibious operation in military history. Meanwhile across the Channel the Germans also gather their strength. Hitler sends one of his best generals, 'the Desert Fox' himself Field Marshal Erwin Rommel, to supervise the construction of coastal defences known as 'the Atlantic Wall'. But the Allies retain one crucial advantage that even Rommel's genius cannot compensate for – only the Allies know where and when they will strike.

D-Day suffers a last minute postponement when the weather over the Channel deteriorates. For Allied Supreme Commander General Eisenhower these are moments of extreme anxiety. Many of his men will be experiencing combat for the first time, and there is much that could go wrong. When meteorologists promise Eisenhower a brief window of improved weather, he takes the gamble and orders the invasion to proceed. Airborne divisions lead the way, parachuting into the darkness over Normandy. Shortly after dawn landing craft approach the coast. At Omaha Beach the Germans are waiting for them. The carnage that follows is described here with vivid personal testimony from both sides.

D-Day is underway, but at Omaha Beach, 'the Bedford Boys', volunteers of the US 29th Infantry Division, find themselves thrown into freezing surf and a murderous German cross-fire. As the first assault waves are mown down on the ramps of their landing craft, it looks like the Allied invasion of Europe might be careering towards disaster. But at other beaches the British, Canadian and US troops are soon able to advance inland. For the local French population it is a moment of joy, but also great danger. Hundreds are killed when the RAF bombs the Norman town of Caen – one of their D-Day objectives. The fighting inland is no less fierce than on the beaches. As 'the Longest Day' draws to a close, rumours circulate on both sides that the enemy is shooting its prisoners.

D-Day is a success, but now the Allies face the challenge of breaking out of the dense hedgerows of Normandy and into open country. They face highly motivated and experienced German soldiers, including Waffen SS units, who make them pay dearly for every yard they advance. The savagery of the fighting also takes a high psychological toll on Allied soldiers – much more so than on German troops who have been subjected to years of indoctrination. But in the end, Allied material superiority takes its toll. General Patton arrives to lead the charge into open country. German soldiers start to surrender in ever greater numbers, and the road to Paris is suddenly open.