By December the Luftwaffe was stronger than it had ever been, numerically. The bomber force had been reduced drastically and its pilots transferred to fighters in home defense squadrons around the Reich. New jet and rocket fighters were beginning to hit the Allied bomber formations. Armed with new weapons, and changed tactics, the German air defenses were again a potential danger.
Their acceptance of battle alternated with periods of stand-down. One of the latter occurred during the early part of December, and it was only one of many clues that the Allied forces had that something was in the offing. Reconnaissance pilots had begun reporting major troop and supply movements on the German side of the lines. Stockpiles appeared, camouflaged in fields and along roads. Trains moved heavy equipment toward the front, and armored columns were spotted, lost and then seen again closer to the battle lines.
It all coalesced in the early morning hours of 16 December, when a German offensive roared into the Ardennes region, driving a deep bulge into the Allied front. The Wehrmacht was back at the top of its old form: Blitzkreig. Armored units slashed into the outnumbered and outmaneuvered Allied defenses, overran the battlefield and pushed about 50 miles (80 km) to the west. It was a desperate attempt to buy time with the slim possibility of destroying several American divisions and perhaps even recapturing Antwerp, with its mountains of supplies and tanks of fuel. It was a brilliant stroke, and it was geared to a long spell of bad weather that grounded most of the Allied counter-air action.
Finally the weather cleared, and a massive counteroffensive began. On the ground, determined drives by American troops started the inexorable retreat of the Germans. The pathetic attempt by the Luftwaffe to seize control of the air was a miserable failure. Allied strategic and tactical air units pulverized rail transport west of the Rhine, halting the forward movement of German reinforcements. By the end of the month, the Wehrmacht was in retreat, and eventually got away without the loss of a single major unit.