After the fall of France and the allied retreat from Dunkirk Hitler proposed an invasion of Great Britain. A secret aerial reconnaissance of the United Kingdom (and all of Europe) had been undertaken by the Luftwaffe several years prior to the outbreak of war, and these images were used in the detailed planning for the invasion of the United Kingdom. After the collapse of the Third Reich the race began to salvage the secrets of Hitler's huge intelligence-gathering operation. The RAF and army intelligence scoured the remains of the Reich, desperately searching for the library of the 'Zentral Archiv Der Fliegerfilm'. The Luftwaffe archive was of extreme value both to the West and the newly emerging superpower of the Soviet Union, under the dictatorship of Stalin. One power held the secrets of both, and competing Soviet and Allied intelligence services searched the debris of the Third Reich for the aerial library. In June 1945 a British intelligence unit stumbled upon 16 tons of reconnaissance pictures, dumped in a barn at Bad Reichenhall, deep in the forests of Bavaria. The original Luftwaffe reconnaissance archive had been destroyed at the end of the war, and this discovery was an incomplete German Army Intelligence copy. The documents were immediately discreetly evacuated back to England, and by July 1945 twenty-three planeloads of documents had been removed from the chaos of Germany to an RAF intelligence clearing house at Medmenham. The entire archive was methodically recorded, sorted, classified as top secret, and removed from public view. Their discovery was not announced and very few were aware of this major find; the archive was locked away in a secure vault, with access restricted to the intelligence services. These records remained classified until 1984, although some escaped into the luggage of returning soldiers who had taken them as souvenirs. It is from this source that Nigel Clarke slowly acquired images, and amassed a collection of over 1,000 surveillance pictures of the UK.