Regiment 2 of Division 324 successively captured heights 224 and 303. On the morning of March 21, Regiment 1 of Division 324 seized Nui Bong, but enemy forces launched a counterattack, leading to intense fighting.
On the morning of March 21, the 2nd Corps Command ordered Regiment 84’s direct-fire artillery unit, stationed at Luoi Cai village temple, to use its firepower to suppress National Highway 1. By the afternoon and night of March 21, Battalions 7, 8, and 2 of Regiment 18, Division 325, maneuvered through forests to attack National Highway 1.
South of Hue, at 5:50 AM on March 21, Regiment 18 (Division 325, 2nd Corps) launched an attack, eliminating enemy forces and securing heights 294, 520, and 560, completely annihilating Battalion 61 of the army of the Republic of Vietnam. Meanwhile, Regiment 101 seized heights 310, 312, and 329.
Fierce fighting took place at height 560, which was only fully secured by 3:00 PM. Artillery forces heavily shelled Ap 5, Dong Toan, Phu Bai, and Mang Ca, while also pinning down enemy forces at La Son, Luong Dien, and Mui Ne.
On the same day, the Tri-Thien Liberation Army attacked enemy positions in Truoi. That night, naval commandos demolished the Thua Luu Bridge, disrupting enemy transport between Hue and Da Nang.
In the direction of Military Region 5, from 5:30 AM to 12 AM on March 21, Division 2 launched an attack, breaking the enemy’s defensive line east of Suoi Da. The enemy rushed Regiment 4 from Chu Lai to reinforce their new defensive line along the Cam Khe-Cha Go-Chop Chai-Tan Loi axis.
In Quang Ngai, starting March 21, local forces completely cut off National Highway 1 between Bac Chau O and Doc Soi. The Quang Ngai Provincial Party Committee called for a mass uprising, leading to the capture of villains and the liberation of enemy-controlled areas. Enemy forces in the province began to fall into disarray.
On March 21, the Central Military Commission, the Ministry of Defence – Commander-in-Chief ordered the Central Highlands Command to advance along the three axes of Highways 19, 7, and 21, working with armed forces and local populations to liberate Binh Dinh, Phu Yen, and Khanh Hoa. Regiment 64 maneuvered to encircle and annihilate enemy forces in Phu Tuc. Battalions 96 and 13 of Phu Yen’s local forces advanced to capture Son Hoa Bridge, east of Cung Son.
In Binh Dinh, Regiment 93 and Tuy Phuoc District armed forces attacked enemy troops in Phuoc Hiep and Cho Huyen. A provincial commando battalion also destroyed the Truong Uc stronghold.
In Phu Yen, local armed forces engaged in fierce battles with enemy troops in Son Hoa and Hon Ken.
On March 21, Military Region 9 received orders from the Regional Command to deploy Division 4 to attack the O Mon-Co Do region.
Along the Truong Son supply route, the Engineer Regiment 99 of the Truong Son Command conducted mine clearance operations and built bridges across the Thach Han River to enable mechanised infantry forces to advance into Thua Thien-Hue from the north. In the southern advance on Hue, Truong Son engineers swiftly repaired the Truoi and Thua Luu bridges, as well as Tuan Ferry, which had been destroyed by retreating enemy forces.
