The 818th supported the 5th Division in fighting around Saarlautern until 19 December, when it was ordered to disengage and move into reserve in response to the German attack in the Ardennes. It was assigned to join the 26th Infantry Division on 21 December; this division had been held in reserve near Metz to refit, and was now being sent north to hold the southern flank of the German offensive as part of III Corps. For the next ten days, the battalion pressed north, with the companies split up among the divisional infantry regiments, until they came to a standstill in Luxembourg at the end of the month. They remained in the line until 27 January, when the division was relieved and returned to the Saarlautern bridgehead.