Northern bank of the Thach Han River (TP Quảng Trị)

 temple, memorial

Hoping to break the stalemate that was developing on the northern front, Lieutenant General Tran Van Quang, commander of the B-4 Front, attacked west from the A Shau Valley toward Hue with the 324B Division. Spoiling attacks by the 1st ARVN Division, however, threw off the timetable.[82] On 28 April the 29th and 803rd PAVN Regiments seized Firebase Bastogne, the strongest anchor on Hue's western flank.[83] This made Firebase Checkmate untenable, and it too was evacuated that night. This exposed Hue to a direct thrust along Route 547. On 2 May PAVN forces south of Hue tried to surround the city.[84]
South Vietnamese northern defense line

The North Vietnamese also attempted to press their attack southward down Highway 1 and across the Thach Han to Hue, but, fortunately for the South Vietnamese, after Truong took command, the 1st and Marine Divisions were reinforced by the 2nd and 3rd Brigades of the Airborne Division (which now totaled three brigades), and the reorganized 1st Ranger Group, raising the ARVN manpower total to 35,000.[85] Also fortuitous was a one-week clearing of the weather, which allowed the application of massive U.S. bombing. The North Vietnamese advance was halted on 5 May.

By mid-May, Truong felt strong enough to go on the offensive in a series of limited attacks, feints, and raids codenamed Song Than (Tidal Wave) that were planned to throw the North Vietnamese off balance, enlarge the defensive perimeter around Hue, and deny the enemy time and space to maneuver.[86] Between 15 and 20 May, Firebases Bastogne and Checkmate were recaptured. PAVN forces then launched another attempt to take the city on 21 May, losing 18 tanks and approximately 800 men in the process. On 25 May a second North Vietnamese assault managed to cross the river, but ARVN defenders put up ferocious resistance, forcing their enemy back across on 29 May.[87] This was the last serious assault on the defenses of Hue. Major General Frederick J. Kroesen, senior U.S. advisor in I Corps, believed that the fall of Quang Tri should have heralded the fall of Hue, but the North Vietnamese had not exploited their opportunity quickly enough. "That he failed completely to take advantage of the moment must be classed as another great blunder of the Quang Tri campaign."[88]

By mid-June, clearing weather allowed more accurate aerial bombardment and shelling from U.S. warships offshore. On the 14th, Truong briefed President Thieu and MACV on his planned counterattack to retake Quang Tri Province. Thieu was not convinced, preferring a smaller-scale operation.[89] The persistent Truong finally convinced the president, emphasizing that such an effort would be possible "employing the superior firepower of our American ally."[90] Thieu finally approved the concept. Truong launched Operation Lam Son 72 on 28 June. The 1st Division continued its westward push toward Laos while the Airborne and Marine Divisions, the 1st Ranger Group, and the 7th Armored Cavalry moved north to retake Quang Tri. The Airborne Division led the way and, utilizing airmobile end-runs and the North Vietnamese were slowly levered out of their defensive positions.[91] The division then advanced to the outskirts of Quang Tri City within ten days, but then President Thieu intervened in the operation. Truong had planned to bypass the city and push on quickly to the Cua Viet River, thereby isolating any PAVN defenders.[92] Thieu, however, now demanded that Quang Tri be taken immediately, seeing the city as "a symbol and a challenge" to his authority.[93]

It was not going to be an easy task for General Truong. The ARVN assault bogged down in the outskirts and the North Vietnamese, appraised of the plans for the offensive, moved the 304th and 208th Divisions to the west to avoid the U.S. airpower that was about to be unleashed upon Quang Tri.[94] The defense of the city and its walled citadel was left to PAVN replacement units and militia. Recalled one participant: "The new recruits came in at dusk. They were dead by dawn...No one had time to check where they were from, or who was their commander."[95] Others described the defense as a "senseless sacrifice" and referred to Quang Tri as "Hamburger City".[95] On 11 July the ARVN Marine Division launched a heli-borne assault north and east of the city which would cut the last remaining road and force the North Vietnamese to reinforce and resupply across the Thach Han River, making them vulnerable to air strikes. After a vicious, three-day battle against the 48th Regiment of the 320B PAVN Division, North Vietnamese forces broke and withdrew.[96]

During the month of July,the ARVN Marine Division was ordered to relieve the Airborne units as the lead element in the battle. But progress was slow, consisting of vicious house-to-house fighting and incessant artillery barrages by both sides. On September the assault to capture the heavily-defended citadel was launched and it was finally taken on 16 September. Truong's forces then advanced to the southern bank of the Thach Han River, where they halted, exhausted and depleted by heavy casualties and unable to push on to Dong Ha.[98]