On this date in the coldest, snowiest weather in 'memory' 3 German Armies, 10 Corps, the equivalent of 29 divisions pushed across the German, Belguim border in the Ardennes forest area starting the Battle of the Bulge.
The Allied forces, after very stiff resistance on the beaches found themselves in a sprint across the low lands, actually gaining territory that they had not expected. It was almost a case of the Allies 'winning' slower than the Germans we 'losing'.
This placed the Allies in a position of having a very long front with very thin manning. They had basically stopped to re-group, bring in more men, guns, ammo, fuel, food and rest the troops prior to a push across the German border.
Into this area of people trying to keep warm and find a hot meal came 3 German Armies.