After the evacuation from Dunkirk in 1940 the Allies knew that to end the Second World War they had to land powerful forces in German-occupied Europe. Four years later on D-Day these landings took place. Why did it take so long, and what were the steps along the way?
Designing, building and moving thousands of vehicles, ships and aircraft took a long time. Millions of men and women had to be trained. Planning for D-Day gathered pace after the United States entered the war in December 1941.
Meanwhile the fighting carried on in other parts of the world.