In the winter of 1941 an alien-seeming object was spotted by an RAF reconnaissance pilot flying a lone unarmed Spitfire across the French coast. Balanced upon the cliffs near Le Havre was what appeared to be a giant convex dish, directed across the Channel at the war-torn British coastline. With Britain's cities being pounded by fearsome bombing raids, teams of experts studied the photograph worriedly. Might the dish constitute a highly secret form of radar - one that had the capacity to tip the balance of the war decisively in the enemy's favour? If so, Nazi Germany would have leapfrogged British technology many-fold. Damien Lewis explains the top-secret mission that was devised to steal what had become known as the 'Wurzburg Dish'.