This programme uses remarkable archive film to tell the story of one of history's most momentous events. It tells the story of how the Allies conceived, developed and finally executed their audacious plan. It looks at the lessons learned in operations such as the disastrous Dieppe Raid, and the successful landings in North Africa and Sicily. The programme also looks at the technologies used including the special tanks that could swim ashore or use flails to create paths through minefields. It also looks at the air campaign and how the Allies were able to enjoy total air superiority without which D-Day might not have happened. Finally, the programme looks at what happened once the Allies were ashore and how it would take over two months to break out from their slender foothold on continental Europe.