After much of Europe had been occupied by the Axis powers for four years, the Allies finally launched their campaign to liberate Western Europe, codenamed Operation Overlord, on 6 June 1944. Over three million service personnel were involved and it all hinged on the success of the Normandy Landings on D-Day.
If the German troops were able to prevent the initial landings, the campaign to liberate Western Europe would fail and German occupation would continue for another year.
Join the Allies as they build up to and execute the largest assault landings ever undertaken in the course of human history.

Launch the animation

http://www.bbc.co.uk/history/worldwars/wwtwo/launch_ani_d_day.shtml