This campaign was from 30 March 1972 to 28 January 1973. On 30 March 1972 the North Vietnamese Army launched its greatest offensive of the entire war. The enemy deployed the greatest array of troops and modern weapons to date in a major effort to end the war with conventional forces and seized considerable territory in an effort to exercise control of key provinces throughout Vietnam.
During this critical period the Vietnamization program continued in the face of the North Vietnamese invasion and the successful counterattack by the armed forces of the Republic of Vietnam. Army aviation units played an impressive role throughout the period, flying reconnaissance, close support missions, and transporting troops. As U.S. combat troops were withdrawn from Vietnam, the role of helicopter units increased in importance and they responded to the challenge of continuing to support while preparing the RVNAF to assume their function. Similarly, advisors of all services contributed immeasurably to the defeat of the enemy invasion and the continued Vietnamization process. Army and Marine advisors fought side-by-side with their RVNAF counterparts to stop and defeat the enemy invasion, as the Vietnamese counteroffensive gained momentum and the reduction of field advisers continued. The advisory effort shifted to emphasize training and to assure that the VNAF attained self-sufficiency prior to the complete withdrawal of the U.S forces.
Recapture of Quang Tri City on 16 September 1972 marked the complete failure of the enemy to hold any of the targeted provincial capitols. Massive aid replaced materiel lost during the spring counteroffensive. Retraining and reconstruction of selected RVNAF units increased their capabilities. The completion of the massive logistical buildup of RVNAF was accomplished, which enabled the RVNAF to become more self-sufficient as direct U.S. participation diminished. The US ground role in Vietnam was totally replaced by the RVNAF. During December 1972 and January 1973 the RVIVAF flew more than 45% of air sorties within Vietnam. In November 1972, the RVNAF began a C-130 training program and by January 1973 realized a significant increase in their capability. RVNAF forward air controllers began directing USAF and RVNAF strike aircraft in January 1973. The US policy of Vietnamization continued.
US combat and combat support operations were conducted in support of RVNAF ground operations during the North Vietnamese invasion and the counteroffensive including intensive interdiction of enemy supply routes into Vietnam. Since US ground forces had been reduced to seven battalions, the US ground combat role was limited to defense of key installations. Further reduction in troop ceilings led to the redeployment of all US ground combat battalions, leaving an Army contingent of combat support and service support units.