 By 13 August , the offensive had fully halted , with German forces being driven out of Mortain . The Panzer Divisions involved lost half of their 150 tanks to Allied counter @-@ attacks and air strikes . As Hitler ordered German forces in Normandy to hold their positions , the U.S. VII and XV Corps were swinging east and north toward Argentan . The German attack west left the 7th Army and Panzergruppe West in danger of being encircled by Allied forces . As American forces advanced on Argentan , British and Canadian forces advanced on Falaise , threatening to cut off both armies in the newly formed Falaise Pocket . 
