The attacks persisted and PAVN forces eventually battered their way into the town, seizing the airfield and reducing the ARVN perimeter to about a square kilometer. During another assault on the 21st, PAVN tanks actually forced their way through the defense perimeter but were held at bay and then destroyed by anti-tank weapons and helicopter gunships. PAVN infantry did, however, manage to seize most of the northern sector of the town, where they began digging in (often right across the street from the ARVN defenders). The initial shock of ARVN troops instilled by North Vietnamese armor was soon abated when they discovered that, because the supporting infantry failed to advance with the tanks, they became easy prey for anti-tank weapons. On other occasions, the opposite would occur, with massed infantry assaults moving forward without armored support. This failure of tactical coordination was one of PAVN's prime weaknesses during the offensive, and one that the allies were quick to exploit.