Although the German high command still considered the Enigma cipher machine secure, they did suspect heavily that the Western Allies were using signal analysis (i.e. studying the frequency or size of intercepted signals to glean information on German intentions) and human intelligence from agents in occupied territory to aid their understanding of upcoming operations. So during the leadup to the Second Ardennes Offensive the Germans sent no signals over radio, but sent individual messengers with orders. Couple this with almost all preparations being prepared on German soil meant there would be very few leaks of human intelligence. The Germans even gave the operation a defensive sounding code name: Die wacht am Rhein (Watch on the Rhine).

So the Germans went out of their way to mount a surprise offensive, and the Americans (and Brits for that matter) fundamentally underestimated German capabilities and intentions. The American 12th Army Group was sending officers on leave and preparing to dig in along the front for the winter after the debacle of Operation Market Garden failed to get the Western Allies into Germany. The only divisions in reserve on the whole Western Front were the Airborne Corps consisting of the 82nd and 101st Airborne Divisions. The Allies had no idea the Germans had been able to assemble such a collection of armor, had the fuel reserves to mount an offensive with them, or would dare to mass their armor together in the face of total allied air superiority.

The Germans managed to gather armor and fuel by starving the Eastern and Italian fronts, stockpiling as much as possible, and running the whole operation on the barest of shoestrings with armored columns being expected to capture Allied fuel and ammo dumps for resupply. The Germans were only able to supply two day's worth of supplies for an all out offensive, and if the timetable was even slightly disrupted the chances of reaching Antwerp were virtually nil. To counter Allied air supremacy, the attack was to be mounted in fog and snow when allied fighters would be grounded.

In the event, the offensive was a shambles despite success the first day. The Germans had little trouble breaking through the weak American front across from them: the four American divisions were either green or had just come out of a nasty battle in a nearby forest that left them depleted and needing reinforcement. One - the first incidentally - of several important communications hubs on the way to the Meuse river was Bastogne, which possessed seven roads in and out of town. Hastily occupied by a brigade of the 10th Armored Division and the under supplied and lightly equipped 101st Airborne Division, the German 5th Panzerarmee threw almost all its strength against Bastogne but failed to either defeat the Americans or force their surrender which totally disrupted the German left flank of the advance. The 6th SS Panzerarmee on the right was checked by Americans and a few Brits dug in along heights to the north if St Vith, and was forced westward away from the Meuse where it too was to be checked when the 2nd Armored division met the 2nd Panzer division and fought them to a standstill.

Meanwhile, the weather cleared and Allied fighters began to hunt down every German tank they could find. The ever energetic Patton had already pulled his third Army out of an eastward attack, and with startling rapidity turned them 90 degrees toward north and set off on a new attack towards Bastogne where the 101st Airborne was successfully holding off a Panzerarmee by itself and kindly brought them supplies to go over to the attack. Hitler declared there would be no retreats from ground gained, and Patton said to Bradley (I paraphrase) the kraut has stuck his head in a meat grinder and I've got my hand on the crank.

At no point, despite the total initial surprise and the confusion sewn in the rear areas by German commando operations, was the offensive seriously likely to succeed. The conditions were too poor, the Germans to shaky logistically and the American Paratroops too stubborn to let the Germans pass.