The weather improved in late December and early January, allowing Allied planes to attack the Germans from the air and seriously hinder their movement. The Germans launched an air offensive of their own in the Netherlands, destroying many Allied aircraft but sacrificing even more of their own irreplaceable aircraft and skilled pilots. They also launched a major ground offensive in Alsace on 1 January, but failed to regain the initiative. The end of Battle of the Bulge is officially considered to be 16 January, exactly one month after the Germans launched it, but fighting continued for three more weeks until early February when the front lines were reestablished on the positions held on 16 December.