 The main German striking force was the XLVII Panzer Corps , with one and a half SS Panzer Divisions and two Wehrmacht Panzer Divisions . Although they made initial gains against the defending U.S. VII Corps , they were soon halted and Allied aircraft inflicted severe losses on the attacking troops , eventually destroying nearly half of the German tanks involved in the attack . Although fighting continued around Mortain for six days , the American forces had regained the initiative within a day of the opening of the German attack . 
