June 6 1944 saw the world’s biggest amphibious assault, one of the most important military campaigns in history and a pivotal moment in the Second World War. For generations, historians, archaeologists and other experts, in their attempts to reconstruct the events of the day, have scoured every battlefield – except one. Just off the coast of Normandy is a lost graveyard, where hundreds of objects lie on the sea bed. Using two mini-submarines, a team of historians, wreck detectives, scientists and veterans are on a quest to discover what lies below the waves. In summer of 2013, the multi-disciplinary team scoured a 500 square kilometre stretch of seabed. Among the astonishing objects they found were a curious collection of American Sherman tanks, specially adapted to float, and the wreck of the SS Leopoldville, a troopship hit by a German U-boat on December 24 1944 with the loss of 800 lives. In an emotional testimony, American D-Day veteran Bill Allen recalls his experiences as a teenage medic on a ship which ferried supplies into Normandy. On his fourth trip to the beaches, his ship hit amine and 94 of his shipmates died. Returning to Normandy for the first time, Bill takes a submarine to the seabed to pay his respects to those comrades who never returned. Submariner Jim Booth, now in his 90s, was part of a key five-man crew manning a midget submarine that lurked off the coast for days before the invasion. At first light on D-Day, they erected a light to guide landing craft safely on to the beach. The expedition team takes him on his first submarine trip since the Normandy landings. D-Day was not only a triumph of individual courage, but also a miracle of detailed planning and engineering brilliance. Tim Beckett’s father Alan was an engineer who had the crucial job of designing a deep sea harbour which would be used to supply the invasion. Tim now teams up with a computer graphics specialist and engineer to build a virtual model of Mulberry Har