Seventy years ago one of the greatest amphibious assaults in history was launched from here on the south coast of England. And within a matter of hours, 7000 vessels had landed 156,000 troops on the beaches of Normandy. It was a manoeuvre that changed the course of the war and tested innovations in science and engineering for the first time. On this programme, engineer Rob Bell looks at the nuts and bolts which made such a staggering invasion possible. From giant troop carrying gliders to tanks that could drive on water. How necessity really did become the mother of invention. Like all new inventions - not all of them worked and resulted in devastating consequences. We find out why. This is the science of D-Day.