In early July 1965, three People's Army of Vietnam (PAVN) regiments (including 32nd and possibly the 33rd) completely isolated the Central Highlands.
On 8 July 1965 Hiếu, II Corps Chief of Staff, was entrusted with the design and execution of a plan to reopen National Route 19.
After sowing confusion among the enemy, Hiếu "press[ed] the Viet Cong from three directions with movements launched from Pleiku and Qui Nhơn and a vertical envelopment from north of An Khê.
These actions resulted in the free flow of cargo convoys during 5 days from D+3 to D+7, "allowing an initial buildup of 5,365 tons of supplies in Pleiku".
[5] After the unsuccessful attempt to overcome the Đức Cơ Special Forces camp in August 1965, General Võ Nguyên Giáp launched the Winter Spring Campaign aiming at cutting South Vietnam in two, from Pleiku in the Central Highlands to Qui Nhơn in the coastal regions.
Division elements will locate and destroy or evacuate enemy foods, ammunition, weapons and medical caches in the operational area.
In preparation for the operation Hiếu with his G3, the CDAT commander and the DCAT G3 made the initial area coordination with General Casey of the 1st Cavalry Division and his G3.
In the end of 1970, Hiếu planned to lure the enemy with a regiment placed in Snuol in Cambodian territory, north of Lộc Ninh on National Route 13.
General Minh, who replaced Trí, did not want to follow through with the luring plan, when 8th Task Force was succeeding in attracting the PAVN who gathered two divisions (5th and 7th) around Snuol.
The beleaguered troops of 8th Task Force, when neither rescue column nor B-52 bombers were in sight, were about to raise the white flag to surrender to the PAVN.
Pushed by both Abrams and Minh to relieve him, Thiệu finally acceded and in April 1971 brought Col. Lê Văn Hưng up from Phong Dinh Province to take over the battered Division.
[11]: 476 Following their incompetent handling of the First Battle of Quảng Trị, both Hiếu and the I Corps commander Hoàng Xuân Lãm were relieved.
Lãm was replaced by Lieutenant general Ngô Quang Trưởng, who succeeded in halting the PAVN advance at the Mỹ Chánh Line.
[11]: 484 In 1974, as Deputy Commander of Operations/III Corps, assistant to General Phạm Quốc Thuần, Hiếu applied Blitzkrieg (lightning war) tactics to alleviate the pressure exerted by the PAVN 5th Division originating from Svay Rieng Province in the Parrot's Beak area of Cambodian territory aiming at Đức Huệ base camp.
[15] Secondly, on April 27, he launched 49th Infantry Regiment and 7th Ranger Group through the swamp lands around Đức Huệ towards the Cambodian border, and had Republic of Vietnam Air Force airplanes attack positions of PAVN 5th Division units.
In the meantime, he relied on two Regional Force battalions belonging to IV Corps to move from Mộc Hóa up north to establish blocking positions on the southwestern edge of the PAVN 5th Division's logistical base and assembly area.
The next morning, three armored squadrons of the III Corps Assault Task Force rushed across the Cambodian border from Gò Dầu Hạ, aiming directly at PAVN 5th Division HQ.
Meanwhile, a task force composing of infantry and armor of IV Corps, originating from Mộc Hóa, maneuvered across the Cambodian border into the Elephant's Foot area to threaten the retreat of the PAVN 275th Regiment.
The three armored squadrons continued their three-pronged advance 16 kilometers deep into the Cambodia before they veered south toward Hậu Nghĩa, and helicopters dropped troops unexpectedly on PAVN positions, while other ARVN units conducted rapid operations into the region between Đức Huệ and Gò Dầu Hạ.
At that time corruption was rampant among the ARVN leadership, in the army, the administration, the police, the power authority, Air Vietnam, customs, etc.
[17] As a result, the Defense Minister, General Nguyễn Văn Vy and seven colonels were ousted and the Military Pension Fund disbanded.
[19]Colonel John Hayes, ARVN 5th Infantry Division Senior Advisor's evaluation on 7 February 1970: MG Nguyen Van Hieu, DOR 1-11-67, 20 years service.
The sources said Maj. Gen. Hiếu was found with a bullet wound in his mouth at his III Corps office at the edge of Biên Hòa airbase, 14 miles (23 km) northeast of Saigon.