The North Vietnamese first struck the flanks of the ARVN column, smashed its outposts, and then moved in on the main ARVN force. Unlike previous encounters during the conflict, the PAVN fielded armored formations, heavy artillery, and large amounts of the latest anti-aircraft artillery. After two months of savage fighting, the ARVN retreated back across the border, closely pursued by the North Vietnamese. One half of the invasion force was killed or captured during the operation, and Vietnamization was seen as a failure.