<Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> Vietnamization received another severe test in the spring of 1972 when the North Vietnamese launched a massive conventional offensive across the Demilitarized Zone . Beginning on March 30, the Easter Offensive (known as the Nguyễn Huệ Offensive to the North Vietnamese) quickly overran the three northernmost provinces of South Vietnam, including the provincial capital of Quảng Trị City . PAVN forces then drove south toward Huế . </P> <P> Early in April, PAVN opened two additional operations . The first, a three - division thrust supported by tanks and heavy artillery, advanced out of Cambodia on April 5 . The North Vietnamese seized the town of Loc Ninh and advanced toward the provincial capital of An Lộc in Bình Long Province . The second new offensive, launched from the tri-border region into the Central Highlands, seized a complex of ARVN outposts near Dak To and then advanced toward Kon Tum, threatening to split South Vietnam in two . </P> <P> 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 . South Vietnam had countered the heaviest attack since Tet, but it was very evident that it was totally dependent on U.S. airpower for its survival . Meanwhile, the withdrawal of American troops, who numbered less than 100,000 at the beginning of the year, was continued as scheduled . By June only six infantry battalions remained . On August 12, the last American ground combat division left the country . However, the U.S. continued to operate the base At Long Binh . Combat patrols continued there until November 11 when the U.S. handed over the base to the South Vietnamese . After this, only 24,000 American troops remained in Vietnam and President Nixon announced that they would stay there until all U.S. POW's were freed . </P>

Involvement of the us in the vietnam war