In December 1944, the Germans launched their surprise Ardennes Offensive, aiming to push towards the port city of Antwerp to deny the Allies an important resupply centre. In what became known as the Battle of the Bulge, the Germans managed to make significant inroads into the Allied defensive line in Belgium and northeastern France. By 20 December, the Germans had advanced on the important road hub of Bastogne, where an assortment of Allied units, bolstered by the reinforcements of the 101st Airborne Division, had been pinned down. The Germans surrounded the Allies on 21 December and cut all inroads to the city. The Allied troops in Bastogne were severely outnumbered and took heavy casualties from German bombing runs and Panzer raids. Aided by the re-routing of German units past the city to continue the push towards Antwerp, units of the US Third Army broke the encirclement from the south on 26 December.