This was the Allied plan for the French resistance forces, with support from the British Special Operations Executive and US Office of Strategic Services, to hinder the road movement of German reinforcements to Normandy after the launch of ‘Overlord’ (6 June 1944).
The undertaking was one of the three elements, together with ‘Vert’ and ‘Violet’ (ii), created for implementation by the Forces Françaises de l’Intérieure, which had come into existence in March 1944 to combine the various resistance forces within occupied France, to slow if not actually to deny the Germans the ability to deliver men and orders into the Normandy area from the rest of occupied France.
The success of this triple effort, and in particular ‘Tortue’ and ‘Vert’, can be attested by just a couple of instances. On 6 June, for example, the German high command ordered SS-Gruppenführer und Generalleutnant der Waffen-SS Heinz Lammerding’s 2nd SS Panzerdivision ‘Das Reich’ to move from Montauban to the Normandy beach-head in what should have been a three-day effort: confined to roads because of railway sabotage and constantly attacked by FFI forces, the division did not arrive at Alençon until 18 June. Generalleutnant Wend von Wietersheim’s 11th Panzerdivision, hastily summoned from the Eastern Front, reached the western border of occupied France in eight days, but then needed another 24 days to cross France from Strasbourg to Caen.