To further enhance their political posture at the Paris talks, which opened on 13 May, the North Vietnamese opened the second phase of the General Offensive in late April. U.S. intelligence sources estimated between February and May the North Vietnamese dispatched 50,000 men down the Ho Chi Minh Trail to replace losses incurred during the earlier fighting. Some of the most prolonged and vicious combat of the war opened on 29 April and lasted until 30 May when the 8,000 men of the 320th PAVN Division, backed by artillery from across the DMZ, threatened the U.S. logistical base at Dong Ha, in northwestern Quảng Trị Province. In what became known as the Battle of Dai Do, the North Vietnamese clashed savagely with U.S. Marine, Army, and ARVN forces before withdrawing. The North Vietnamese lost an estimated 2,100 men after inflicting casualties on the allies of 290 killed and 946 wounded.
During the early morning hours of 4 May, communist units initiated the second phase of the offensive (known by the South Vietnamese and Americans as “Mini-Tet”) by striking 119 targets throughout South Vietnam, including Saigon. This time, however, allied intelligence was better prepared, stripping away the element of surprise. Most of the communist forces were intercepted by allied screening elements before they reached their targets. 13 Viet Cong battalions, however, managed to slip through the cordon and once again plunged the capital into chaos. Severe fighting occurred at Phu Lam, (where it took two days to root out the 267th Viet Cong Local Force Battalion), around the Y-Bridge, and at Tan Son Nhut. By 12 May, however, it was all over. Vietcong forces withdrew from the area leaving behind over 3,000 dead.
The fighting had no sooner died down around Saigon than U.S. forces in Quang Tin Province suffered what was, without doubt, the most serious American defeat of the war. On 10 May two regiments of the 2nd PAVN Division attacked Kham Duc, the last Special Forces border surveillance camp in I Corps. 1,800 U.S. and South Vietnamese troops were isolated and under intense attack when MACV made the decision to avoid a situation reminiscent of that at Khe Sanh. Kham Duc was evacuated by air while under fire, and abandoned to the North Vietnamese.
The communists returned to Saigon on 25 May and launched a second wave of attacks on the city. The fighting during this phase differed from Tet Mau Than and “Mini-Tet” in that no U.S. installations were attacked. During this series of actions, Viet Cong forces occupied six Buddhist pagodas in the mistaken belief that they would be immune from artillery and air attack. The fiercest fighting once again took place in Cholon. One notable event occurred on 18 June when 152 members of the Viet Cong’s Quyet Thang Regiment surrendered to ARVN forces, the largest communist surrender of the war. The actions also brought more death and suffering to the city’s inhabitants. A further 87,000 were made homeless while more than 500 were killed and another 4,500 were wounded. During the second phase (5 May – 30 May) U.S. casualties amounted to 1,161 killed and 3,954 wounded, while 143 South Vietnamese servicemen were killed and another 643 were wounded.