Troops from the UK, the US, Canada, and France attacked German forces on the coast of northern France, on 6 June 1944.
It was the largest military naval, air and land operation ever attempted and marked the start of the campaign to liberate Nazi-occupied north-west Europe.
D-Day involved the simultaneous landing of tens of thousands of troops on five separate beaches in Normandy.
Airborne troops were dropped behind enemy lines in the early hours, while thousands of ships gathered off the Normandy coast for the main attack.
Though they were expecting an invasion, German military leaders believed the initial attacks were only a diversionary tactic.
A deception plan in the weeks ahead of the attack had led them to expect the main invasion further along the coast.
The surprise element helped British troops establish a foothold on a beach codenamed Gold.
In addition, Canadian forces established themselves on another beach – Juno – and the British got on to Sword beach.
American soldiers also managed to land on the westernmost beach – Utah – without major casualties.
The defeat of Germany was acknowledged as the western Allies’ principal war aim as early as December 1941. Opening a second front would relieve pressure on the Soviet Union in the east and the liberation of France would weaken Germany’s overall position in western Europe. The invasion, if successful, would drain German resources and block access to key military sites. Securing a bridgehead in Normandy would allow the Allies to establish a viable presence in northern Europe for the first time since 1940.
A command team led by American General Dwight D. Eisenhower was formed in December 1943 to plan the naval, air and land operations. Deception campaigns were developed to draw German attention – and strength – away from Normandy. To build up resources for the invasion, British factories increased production and in the first half of 1944 approximately 9 million tonnes of supplies and equipment crossed the Atlantic from North America to Britain. A substantial Canadian force had been building up in Britain since December 1939 and over 1.4 million American servicemen arrived during 1943 and 1944 to take part in the landings.
The invasion was conducted in two main phases – an airborne assault and amphibious landings. Shortly after midnight on 6 June, over 18,000 Allied paratroopers were dropped into the invasion area to provide tactical support for infantry divisions on the beaches. Allied air forces flew over 14,000 sorties in support of the landings and, having secured air supremacy prior to the invasion, many of these flights were unchallenged by the Luftwaffe.
Members of the French Resistance and the British Special Operations Executive (SOE) provided intelligence and helped weaken defences through sabotage. The Allied deception campaigns succeeded in convincing the Germans as late as July 1944 that the main invasion force would still land elsewhere. The threat of this larger, second invasion kept German reinforcements tied down away from Normandy. Defence also suffered from the complex and often confused command structure of the German Army as well as the constant interference of Adolf Hitler in military matters. However, the Allies faced a number of setbacks both on 6 June and in the months that followed. On D-Day, the Americans came close to defeat on Omaha partially because the preliminary air and naval bombardment failed to knock out strong defence points, but also because they faced highly effective German troops who had gained hard-earned experience on the Eastern Front. Throughout the Battle of Normandy, the technical superiority of their tanks and anti-tank weapons, as well as the tactical skill of their commanders, gave German forces an advantage over the Allies. However, the Germans were never able to fully exploit their successes or the weaknesses of the Allies in a decisive way.