The Battle of the Mỹ Chánh Line took place from 5 May to 26 June 1972 during the People’s Army of Vietnam (PAVN)'s Easter Offensive of the Vietnam War. South Vietnamese forces, principally the Marine Division, with extensive fire and logistics support from United States forces, succeeded in stopping the PAVN advance northwest of Huế and launched a series of spoiling attacks against PAVN units. The successful defense allowed South Vietnamese forces to build up strength and then establish jumping off positions for their counteroffensive to recapture Quảng Trị Province.
Background At the end of the First Battle of Quảng Trị, Army of the Republic of Vietnam (ARVN) forces retreated south towards Huế. The Marine Division (VNMC) 369th Marine Brigade, led by Colonel Pham Van Huang, held two bridges on Highway 1 with the 9th Battalion holding the Song O-Khe bridge and the 5th Battalion holding the Song Tach Ma bridge. At dawn on 3 May the PAVN launched an artillery barrage and then attacked the Song O-Khe bridge with 18 T-54 tanks and infantry. The Marines destroyed 17 tanks and killed hundreds of PAVN before blowing up the bridge and falling back to form a defensive line northwest of Huế along the south bank of the Mỹ Chánh River.
On 4 May, the South Vietnamese Joint General Staff replaced the ineffective General Hoàng Xuân Lãm as I Corps commander with Lieutenant General Ngô Quang Trưởng. Trưởng moved his main command post to the Huế Citadel, a move that reflected a change in purpose and focus for operations in Military Region I (MR I). His immediate task was to stabilize his forces and to make effective use of available American support through 1st Regional Assistance Command (FRAC) which had replaced the United States Army's XXIV Corps. On the same date, President Nguyễn Văn Thiệu announced the appointment of Colonel Bui The Lan, as interim VNMC commander. Thiệu's order of the day was that the Mỹ Chánh Line would hold; there would be no further withdrawals.
Trưởng's available forces initially included elements of the VNMC north and northwest of Huế, the 1st Division south and southwest of Huế blocking any further PAVN advance from the A Sầu Valley and the 2nd Division in MR I's southern provinces. The remainder of the VNMC was later deployed to Huế and was given responsibility for north and northwest Thừa Thiên Province.
As the PAVN offensive halted at the Mỹ Chánh River, everything to the north was declared a free-fire zone. FRAC believed that the PAVN were capable of launching a new offensive in Thừa Thiên Province as the 304th, 308th and 324B Divisions, the 202nd and 203rd Armored Regiments and supporting units were all available for an assault. From 5 to 25 May, the PAVN probed the river-edge defenses. Losses sustained in the previous weeks did not permit full-scale offensive actions, but the PAVN's intentions were clear. Huế was the target and a major assault of the Mỹ Chánh Line was imminent.
Battle On 5 May, the Marine 258th Brigade displaced its headquarters north from Huế to Phong Điền on Highway 1 to relieve the headquarters of Marine 369th Brigade. It was a shift of headquarters only, as the respective battalions remained in place and the 39th Ranger Battalion assumed control of Camp Evans. Brigade commander Lieutenant Colonel Ngo Van Dinh concentrated his 2nd Battalion at the junction of Highway 1 and the Mỹ Chánh River in order to prevent any attempted by the PAVN to reconstruct the highway bridge that had been destroyed earlier. Dinh heavily reinforced his western flank as he anticipated the all-out attack on Huế to originate in the nearby foothills. The area to the west, due to thick canopy and rolling hills, was well concealed from aerial observation. The Marines of the 258th Brigade were thinly spread over a large area, but Dinh was confident. He kept his units moving, effectively employing the principle of economy of force by concentrating his forces only as PAVN threats developed.
The 369th Brigade assumed operational control of the eastern half of the division's area of the Mỹ Chánh Line, including the Regional and Popular Force units responsible for the area near the coast. This drastically reduced the 369th Brigade's area of responsibility and the Mỹ Chánh Line was stronger than ever. The 147th Brigade remained at Huế with the 4th and 8th Battalions, replacing personnel and making up supply losses sustained in the First Battle of Quảng Trị. Replacement equipment came directly from United States Marine Corps (USMC) stocks. New antitank weapons arrived to augment the Marine capabilities to defeat armor on the ground.
Trưởng arranged for the Direct Air Support Center at Da Nang Air Base to move forward to Huế and a fire support coordination center (FSCC) was colocated to coordinate artillery, naval and air support. Trưởng established priority targets for air support as: 1. 130mm guns: 2. tanks; 3. smaller artillery; and 4. trucks. In addition U.S. air power spent the first week of May destroying abandoned equipment along Highway 1 and at Firebase Nancy and destroying 45 bridges north of Mỹ Chánh. The 130 mm guns proved especially difficult as they were well deployed, making it difficult for the observers to get a fix on firing positions. Due to the SA-7 antiaircraft missile threat, airborne Forward Air Controllers (FACs), forced to fly above , could not readily spot enemy gun flashes. The PAVN guns had no more than two platoons (two to four guns) in any one position. These were spread all over the northwest portion of Quảng Trị Province. As FACs flew over suspected PAVN gun positions, the guns would cease firing and another platoon would open up from a different sector, linked by an efficient communications network.
After having overrun Firebase Bastogne and Firebase Checkmate at the end of April, on 5 May the PAVN 324B Division attempted to continue their advance down Route 547 towards Huế and in two clashes west and southwest of Firebase Birmingham, 39 PAVN and two ARVN were killed.
On 8 May the 2nd Airborne Brigade arrived at Huế and came under the operational control of the VNMC. With increasing forces available, Trưởng planned a series of limited objective attacks and raids to provide the South Vietnamese time to prepare for their counteroffensive and keep the PAVN off balance. The South Vietnamese gave the code name Song Than (Tidal Wave) to these operations. The first operation named Song Than 5-72 was to be a helicopter raid against PAVN positions in the Hải Lăng District southeast of Quảng Trị.
Operation Song Than 5-72 During darkness on 12 May, the 369th Brigade's reconnaissance company, the communications officer of the 9th Battalion and a small group of other Marines swam the Mỹ Chánh River to establish a communications site to assist command and control of the operation the next morning. CH-46s and CH-53s from HMM-164, part of the USMC 9th Marine Amphibious Brigade (9th MAB) operating off the coast of South Vietnam, then lifted 1,138 Marines into attack positions. To move the two battalions, 60 marines were carried by each CH-53 and 20 by each CH-46 in two sequential waves. HMM-164 planned to provide the maximum possible lift capability in each wave and to reduce possible losses, the helicopter assault routes were flown Nap-of-the-earth contrary to then-current practice. The CH-46s were to be to above ground and the CH-53s only slightly higher. Six AH-1G Cobras, two OH-6As and a UH-1 of the Army's Troop F, 4th Cavalry (Air Cavalry) flying from Phu Bai Combat Base provided armed escort. A single wave of helicopters was used for each of two landing zones, reducing the exposure time to PAVN antiaircraft fire. The helicopters proceeded to Fire Base Sally to load the 3rd and 8th Battalions, 369th Brigade.
The two landing zones received devastating fire from the air and sea. As a result, touchdown in Landing Zone Tango () occurred at 09:30 without opposition in a cloud of dust and smoke. The Marine helicopters returned to the ships for fuel then flew back to Firebase Sally for the second wave at 10:55. As the lead aircraft touched down in Landing Zone Delta moderate small-arms fire was received. Immediately, the Army commander of the escorting gunships shifted the landing to the southern portion of the zone. The PAVN hit three CH-46s and Marine airmen left one CH-53 in the zone with a damaged tail rotor which had to be destroyed to prevent its capture.
Once on the ground, the two battalions swept south and attacked toward the Mỹ Chánh River. Shortly thereafter, the 9th Battalion crossed the Mỹ Chánh and attacked north toward its two sister battalions. The PAVN 66th Regiment was caught completely by surprise. As the two battalions marched south to link up with the 9th Battalion, they uncovered large quantities of combat equipment and freed more than 150 civilians who had been detained by the PAVN. The joint efforts resulted in reports of 240 PAVN soldiers killed, three tanks destroyed and two 130 mm guns put out of action.
On 14 May approximately 4,000 ARVN 1st Division troops supported by artillery and B-52 strikes advanced west from Firebase Birmingham along Route 547 coming to within of Firebase Bastogne and killed 110 PAVN.
PAVN attack 21–2 May On 21 May the PAVN mounted a full-scale armor and infantry attack on the Mỹ Chánh Line in an attempt to regain the initiative. The PAVN attacked due south down the coastal highway, Route 555, () moved across the Mỹ Chánh River and penetrated the 369th Brigade's defensive area. The Regional Force troops fell back, exposing the flanks of the 3rd and 9th Battalions. Vulnerable to the overwhelming armor threat, both battalions withdrew. After an all-day fight, however, the two battalions, assisted by close air strikes and ARVN armored cavalry, began pushing the PAVN back towards the Mỹ Chánh River. The Marines had suffered heavy casualties but by nightfall had largely restored the line.
The PAVN remained determined to gain a foothold on the south bank of the river. At 01:00 on 22 May, the PAVN launched a tank-infantry attack against the 3rd Battalion. They had the initiative and the numerically superior force, supported by 25 tanks, overran the forward battalion, but not before the Marines had destroyed eight tanks with M72 LAWs and direct fire from 105mm howitzers. Continuing their attack through the early morning darkness, the PAVN penetrated deeply into South Vietnamese territory, hitting the 369th Brigade's command post at first light. A U.S. Army sergeant fired the BGM-71 TOW missile system from atop the command and control center bunker destroying a PT-76 and then a heavy machine gun nest. Five PAVN armored vehicles came within 400 meters of the command post before being destroyed. By 09:30, a total of 10 tanks and armored personnel carriers had been destroyed. As the 8th Battalion counterattacked, the PAVN fled the battlefield, leaving their dead and wounded.
Operation Song Than 6-72 On 23 May, the 7th Battalion and its advisors moved by truck to Tân Mỹ Base where it boarded landing craft for the short trip to the ships of the U.S. amphibious force: the , , and in preparation for Operation Song Than 6-72 an amphibious assault at Wunder Beach 10 km north of the Mỹ Chánh Line and a heliborne assault 6 km inland. The operation was coordinated onboard by the 147th Brigade and 9th MAB staff.