South Vietnam's ground war, 1972-1975

After the full implementation of the Vietnamization doctrine, the U.S. saw the Army of the Republic of Viet Nam as taking responsibility for ground combat in South Vietnam, with both direct air and naval combat support from U.S. forces, as well as combat support in areas such as intelligence and communications, and combat service support in supply and maintenance.

In the face of declining U.S. popular support of the war, the Nixon Administration had adopted the Vietnamization doctrine, in which U.S. ground troops would no longer fight in South Vietnam, although, consistent with negotiations with the Communists, there would be U.S. foreign military assistance to the South, and always the threat of U.S. air and naval attacks against the North.

Nixon's larger strategy was to convince Moscow and Bejing they could curry American favor by reducing or ending their military support of Hanoi. He assumed that would drastically reduce Hanoi's threat. Second, "Vietnamization" would replace attrition. Vietnamization meant heavily arming the ARVN and turning all military operations over to it; all American troops would go home.

By 1972, the North Vietnamese committed to a conventional invasion against the South. While it was repelled, the eventual Paris treaty further restricted U.S. involvement, and the endgame came with a new [[conventional invasion in 1975.

1971
The Vietnamization policy achieved limited rollback of Communist gains inside South Vietnam only, and was primarily aimed at providing the arms, training and funding for the South to fight and win its own war, if it had the courage and commitment to do so. By 1971 the Communists lost control of most, but not all, of the areas they had controlled in the South in 1967. The Communists still controlled many remote jungle and mountain districts, especially areas that protected the Ho Chi Minh Trail.

Saigon's effort to strike against one of these strongholds, Operation Lam Son 719, was a humiliating failure in 1971. The SVN forces, with some U.S. air support, were unable to defeat PAVN regulars.

1972
In March, 1972 Hanoi invaded at three points from north and west with 120,000 PAVN regulars spearheaded by tanks. This was conventional warfare, reminiscent of North Korea's invasion in 1950. They expected the peasants to rise up and overthrow the government; they did not. They expected the South's army to collapse; instead the ARVN fought very well indeed. Saigon had started to exert itself; new draft laws produced over one million well-armed regular soldiers, and another four million in part-time, lightly armed self-defense militia.

Eastertide invasion
North Vietnam began preparing the battlefield for its major invasion, by establishing an air defense network to protect what was to be their rear areas, north of the DMZ. This included S-75 Dvina (NATO reporting name SA-2 GUIDELINE) surface-to-air missiles that shot down three U.S. fighter-bombers in February.

The main attack came with the start of the monsoon season, which prevented close air support and even good artillery fire control.

Operations in the North (RVN I Corps area)
The northern operation, launched on March 31, used three divisions for the attack, followed later by another three divisions. The PAVN 308th & 304th Divisions moved into Quang Tri province, followed by the 324B division attacking ARVN positions west of Hue.

Facing them was the newly formed 3rd ARVN Division, reinforced with the 147th Marine Brigade, 1st Airbone Brigade (detached from the Airborne Division), and 5th Armored Brigade. This was an odd mixture of troops for a critical area; the 3rd Division had only one regiment of experienced soldiers, while its other two regiments were made up of troops "who had been sent to the northernmost province of SVN as a punishment." While the RVN Marines and Airborne had excellent reputations, this did not even comply with the 1975 "light at the top, heavy at the bottom" force dispositions. An army may place low-quality troops on a border, to pin the enemy while more powerful and mobile units maneuver for a counterattack.

These forces fell back, first to Dong Ha. They then linked to a defense line manned by the rest of the Airborne Division and another Marine brigade, south of the My Chanh River.

May stabilization
Improvements in the weather allowed the U.S. to interdict the PAVN supply lines, and their offensive slowed; they moved back to secure an area south of the DMZ. This area was proclaimed under the control of the "Provisional Revolutionary Government of South Vietnam" (PRG). it welcomed diplomats from the Communist world, including Fidel Castro, and served as one of the launch points of the 1975 invasion. The PRG areas now contained five PAVN divisions.

July counterattack
Some ground north of My Chanh was regained by the Airborne Division on the East and Marine Division on the West.

On September 14, the RVN Marines reentered Quang Tri.

The RVN relaxes
After the failed Easter Offensive the Thieu government made a fatal strategic mistake, going to a static defense and not refining its command and control for efficiency, not political reward. The departure of American forces and American money lowered morale in both military and civilian South Vietnam. Desertions rose as military performance indicators sank, and no longer was the US looking over the shoulder demanding improvement.

On other side, the PAVN had been badly mauled--the difference was that it knew it and it was determined to rebuild. Discarding guerrilla tactics, Giap three years to rebuild his forces into a strong conventional army. Without constant American bombing it was possible to solve the logistics problem by modernizing the Ho Chi Minh trail with 12,000 more miles of roads, as well as a fuel pipeline along the Trail to bring in gasoline for the next invasion.