 The U.S. countered with a buildup of American airpower to support ARVN defensive operations and to conduct Operation Linebacker, the first offensive bombing of North Vietnam since "Rolling Thunder" had been terminated in 1968.The PAVN attacks against Huế, An Lộc, and Kon Tum were contained and the ARVN launched a counteroffensive in May to retake the lost northern provinces.On September 10, the South Vietnamese flag once again flew over the ruins of the Citadel of Quảng Trị City, but the ARVN offensive then ran out of steam, conceding the rest of the occupied territory to the North Vietnamese.