Around 1943, as the French Resistance grew in size (due to the Vichy regime accepting the deportation of Frenchmen for forced labor in Germany), German anti-partisan operations in France became more serious. In response, Germans deployed military units against the resistance groups. Further, Germans managed to create a large and successful counter-network of covert collaborators, which succeeded in infiltrating many cells of the French resistance. The first major German military operation against the French Resistance took place in early 1944 in the mountainous region of the French Alps and French Jura. The French resistance forces went to ground and reorganized soon after the German operation ended. Soon afterward, another operation where the French Resistance challenged the Germans to a battle at Plateau de Glieres in Savoy ended in a German victory. Despite this defeat and London's advice to avoid head-on confrontation, in the aftermath of the Allied invasion of France (D-Day) the French Resistance openly challenged German forces in several areas. After several early Resistance successes, German countermeasures became particularly harsh. Once seriously threatened, German forces resorted to brutality and terror that had been mostly unheard of previously in the Western front (but commonplace on the Eastern). The largest atrocity occurred in Oradour-sur-Glane, where the Germans massacred 642 local inhabitants and burned the village. German terror tactics proved successful in the short term, as the shocked Resistance pulled back.