More than 60 years ago, the outcome of World War Two rested heavily on five beaches in Normandy, France. Known as 'D-Day', it is considered the greatest amphibious invasion ever attempted. History remembers it as a great victory. But new research reveals that on Omaha Beach, it was very nearly a disaster. German defences there were far more ferocious than expected. A massive air strike which had intended to take them out was a total failure. For the troops charged with this mission, it would become a killing zone.