How did so few men manage to organize resistance networks and gather so much intelligence in such a short time despite being unceasingly hunted by the German and Vichy counterespionage services?It is thought that 70% of the information which was vital for the Allies before the Normandy landings in 1944 was sent by French agents working for the BCRA.Using very often unpublished or ignored documents, the author gives an account of General de Gaulle's secret services which, in 1940, were thought to be just a small group of amateurs but which as the war progressed, became a powerful war machine in the service of the Free French.