Hanoi had committed 14 divisions and 26 independent regiments to the offensive and had suffered approximately 100,000 casualties and lost almost all of its armored forces committed (134 T-54s, 56 PT-76s and 60 T-34s). In return, it had gained permanent control of half of the four northernmost provinces (Quảng Trị, Thừa Thiên, Quảng Nam, and Quảng Tín) as well as the western fringes of the II and III Corps sectors, around 10% of the country. It is believed that the North Vietnamese leadership had both underestimated the fighting ability of the ARVN, which, by 1972, had become one of the best-equipped armies in the world, and failed to grasp the destructiveness of American air power against an enemy fighting a conventional battle. Combined with these strategic errors, PAVN commanders had also thrown away their local numerical superiority by making frontal attacks into heavy defensive fire and suffered massive casualties as a consequence. However, by its own estimate, the PAVN had also dealt the most severe blow in the entire war, with over 200,000 ARVN casualties, a third of the South's entire armed forces. That also allowed Viet Cong irregulars and political agents to make a return through the gaps in the defensive lines, which had been torn open during the offensive. Hanoi wasted no time in making use of what it had gained. The North Vietnamese immediately began to extend their supply corridors from Laos and Cambodia into South Vietnam. The PAVN rapidly expanded port facilities at the captured town of Đông Hà, and within a year, over 20 percent of the materiel destined for the southern battlefield was flowing across its docks.