The Mỹ Chánh River is not an imposing geographic barrier. It runs east toward the South China Sea, its banks low and cultivated in peacetime. What made it defensible in May 1972 was less the river itself than the Vietnamese Marine Division — the VNMC — and the decision to stop retreating. The 369th Marine Brigade, commanded by Colonel Pham Van Huang, had conducted the rearguard action during the collapse. On the morning of May 3rd, PAVN forces attacked with 18 T-54 tanks and infantry at the Song O-Khe bridge on Highway 1. The Marines destroyed 17 of those tanks before blowing the bridge themselves and falling back to the south bank of the Mỹ Chánh. It was a fighting withdrawal, not a rout — and it established the tone for what was coming.

On May 3rd, the South Vietnamese Joint General Staff made a decision that would prove decisive. General Hoàng Xuân Lãm, whose handling of I Corps had been widely criticized as ineffective, was replaced as commander by Lieutenant General Ngô Quang Trưởng. Trưởng was by most assessments one of the most capable officers in the ARVN — disciplined, respected by his soldiers, and possessed of a clearer operational sense than his predecessor. He moved his main command post to the Huế Citadel, a physical statement of purpose: the ancient imperial city would not fall. Trưởng's immediate task was to stabilize a force that had just experienced catastrophic defeat and make effective use of the American support available through the 1st Regional Assistance Command. The 2nd Airborne Brigade arrived in Huế on May 8th, adding to the forces under his command.

Rather than simply waiting for the next PAVN assault, Trưởng launched a series of limited offensive operations he code-named Song Than — Tidal Wave. These were raids and helicopter assaults against PAVN positions, designed to keep the enemy off balance and buy time to rebuild South Vietnamese strength. The first, Song Than 5-72, targeted PAVN positions in the Hải Lăng District southeast of Quảng Trị. Throughout May, the PAVN probed the river-line defenses but could not mount a full offensive — their losses in the first weeks of the Easter Offensive had been severe, and resupply across the extended North Vietnamese logistics chain was strained. From the PAVN's own internal assessments, quoted in Vietnamese military histories, "our troops experienced many difficulties in maintaining supply levels and we were able to provide only 30 percent of the supplies called for in our plan."

The PAVN's patience ran out on May 21st. A full-scale armor and infantry assault pushed south down Route 555 along the coast, crossed the Mỹ Chánh, and penetrated the 369th Brigade's defensive sector. Regional Force troops, less experienced than the Marines, fell back under the pressure — and their withdrawal exposed the flanks of the Marine 3rd and 9th Battalions, who also pulled back under the threat of being surrounded. For a time the line looked as if it might dissolve entirely. Then, with close air support and ARVN armored cavalry assisting, the two Marine battalions counterattacked and began pushing the PAVN back toward the river. By nightfall the line had been largely restored. The Marines had absorbed heavy casualties. So had the PAVN. Further assaults on June 23rd and 24th were repulsed with significant losses — 13 tanks destroyed on the 23rd, 22 more on the 24th, and over 100 North Vietnamese soldiers killed in each action.

By late June 1972, the probing attacks had served Trưởng's purpose, whether or not that was their only intent. South Vietnamese forces had rebuilt their strength, identified PAVN dispositions, and established forward positions from which to launch a counteroffensive. On June 28th, Operation Lam Son 72 began — the drive north to retake Quảng Trị Province and, at its center, the citadel in Quảng Trị town. The PAVN's own analysis of what happened at the Mỹ Chánh was frank: "because we had been slow to change our campaign tactics as the enemy strengthened his forces and solidified his defense, our assault against the Mỹ Chánh defensive line from 20 to 26 June was unsuccessful." The line had held. For the soldiers who had held it — and for the civilians of Huế who had spent those weeks wondering if the city would fall as Quảng Trị had — that outcome was everything.