In the New Mexico desert, a secret team of scientists is working flat out to develop atomic bombs. It's the most important American military project in history. But one of those scientists lives a double life. Klaus Fuchs has decided to betray his country and share America's most secret technology with the Soviet Union. But is he the only person who has turned traitor?

In a re-upload of one of our D-Day 24 Hour videos, Astrid introduces you to the war's most effective counter-espionage and deception programme, The Double Cross system. Today she'll talk about their operations before and during D-Day and introduce you to some of the most important double agents. Their mission - fool the Führer.