The Division was formed on 20 October 1965 from the 1st Regiment and the 21st Regiment which had just arrived from North Vietnam. The Division was under the command of the PAVN B1 Front. In February 1967 the Division's 21st Regiment was engaged by South Korean forces, losing over 1000 killed in 2 separate battles northwest of Quảng Ngãi. From 21 April to 5 June 1967, the Division was the target of US Marine Corps' Operations Union and Union II in the Quế Sơn Valley losing over 1,400 killed. In early August 1967 the Division's 1st and 21st Regiments were the target of Operation Hood River, losing 166 killed. In September 1967 the B1 Front ordered the Division back into the Quế Sơn Valley. In September 1967 the Division was the target of Operation Wheeler. On 5 December 1967 a command group from the Division was carrying out reconnaissance near Firebase Ross when they were attacked by US helicopter gunships, losing 17 killed including the Division commander, Senior Colonel Le Tru Huu, the division’s political officer, its deputy chief of staff, its chief of rear services, its chief of military operations and intelligence, its chief of combat operations and training, and the commanders of the 3rd and 21st Regiments along with several of their battalion commanders. On 9 December the Division's 3rd Regiment was engaged by US helicopter gunships near Landing Zone Baldy, losing 121 killed. Senior Col. Giap Van Cuong, a former commander of the 3rd Division, became the Division’s new commander and was given orders to destroy the US 3rd Brigade, 1st Cavalry Division. On the afternoon of 2 January, elements of the 12th Cavalry Regiment engaged a unit of the Division in a four-hour-long battle 5 km south of Ross resulting in 3 U.S. and 39 PAVN killed. On the early morning of 3 January the PAVN attacked four U.S. firebases in the Quế Sơn Valley, launching ground attacks against Ross and Landing Zone Leslie, which were defeated by dawn for the loss of 18 U.S. and 331 PAVN killed. On 7 January, Division anti-aircraft gunners shot down a helicopter carrying the commander of the 2nd Battalion, 12th Cavalry, Lt. Col. Robert L. Gregory, killing him and six others on board. On 10 January the 2/12th Cavalry, engaged a reinforced battalion of the Division near Firebase Ross resulting in 122 PAVN killed. In total the Division had lost more than 1,100 soldiers killed in action between December and January. For the Tet Offensive of January/February 1968 the Division was to attack Da Nang however its slow approach to the city meant that it was still 25km away on 30 January. As the Division approached Da Nang on 31 January, its 8th Battalion, 31st Regiment, attacked the district capital of Điện Bàn, but the attack was resisted by ARVN troops and Korean Marines. On 3 February when the ARVN 51st Regiment swept through Thanh Quit, they stumbled onto a battalion from the 31st Regiment hidden there and engaged them in battle, supported by the Korean marines until they broke contact at nightfall. On 6 February the Division began a concerted push north towards Da Nang. At 03:00 the 21st Regiment attacked the ARVN 51st Regiment's base camp, the ARVN were reinforced by US Marines and the fighting continued until the PAVN withdrew at nightfall on 7 February with losses estimated at more than 586 killed. Following the Battle of Lo Giang on 8-9 February a combined US Army/Marine task force named Task Force Miracle pursued the Division as it withdrew to its base areas near Go Noi Island killing 236 PAVN/VC soldiers near there on 9 February. In total the Division had lost 1,200-1,400 soldiers in the period from 29 January to 14 February 1968 and had completely failed to penetrate Da Nang. After the Division had recuperated from its Tet losses, between 10 and 12 May 1968, 2 of its Regiments successfully captured Kham Duc. In July 1968 the Division's 1st Regiment was the target of Operation Pocahontas Forest in the Quế Sơn Valley in which it lost 127 killed. During the Phase III Offensive a regiment of the Division was ordered to attack Tam Kỳ. During the War of the flags in January/February 1973 the Division briefly captured Sa Huỳnh Base and stretch of Highway 1 before being ejected by ARVN forces by 16 February. During the 1975 Spring Offensive the Division was tasked with attacking Tam Kỳ and then moving north to threaten the southern approaches to Da Nang. On 21 March the Division began attacking the outer defenses of Tam Kỳ and by 24 March following an artillery barrage, began their attack on the city, quickly penetrating the western and southern defenses. The ARVN defenses soon broke with some ARVN units being evacuated by helicopters from the beach while others fled north and south along Highway 1. Following the capture of Tam Kỳ, the Division moved north along Highway 1 bypassing ARVN defensive positions and together with other PAVN columns entered Da Nang on the morning of 29 March. On 5 April the Division was ordered to remain and secure Quảng Nam and Quảng Tín Provinces while other PAVN units moved south to join the assault on Saigon.
