The Germans thought they had an extensive network of spies operating in the UK, but in fact, all their agents had been captured, and some had become double agents working for the Allies as part of the Double-Cross System. The double agent Juan Pujol García, a Spanish opponent of the Nazis known by the code name "Garbo", developed over the two years leading up to D-Day a fake network of informants that the Germans believed were collecting intelligence on their behalf. In the months preceding D-Day, Pujol sent hundreds of messages to his superiors in Madrid, messages specially prepared by the British intelligence service to convince the Germans that the attack would come in July at Calais.