Rees was parachuted in southern France in April 1943 with the specific task of building up the resistance movement in the Jura region of France. Rees was involved in the blowing up of the Peugeot works in France – having been given the permission to do this by Rudolphe Peugeot during a personnel interview. The Peugeot works were considered to be the third most important target in France and raids by Bomber Command had failed to destroy this factory. In November 1943, Rees was wounded in a fire fight with a Gestapo official. Sympathetic French people hid him until he could return to London, via Spain. Rees arrived in London in July 1944.