On 23 February 1967, Badcoe and his United States Marine Corps deputy, Captain James Custar, were advising an RF company operation in the Phu Thu District. About 660 yards (600 m) on their flank was a PF platoon accompanied by two United States Army advisers, Captain Clement and Sergeant Thomas. Badcoe and Custar began to hear intermittent rifle fire, coming from the direction of the flanking platoon. Custar was monitoring radio transmissions when he heard that Clement had been wounded and Thomas was in danger. Badcoe ran across the intervening fire-swept ground to reach the PF platoon, with the enemy fire intensifying as he approached. He discovered that Clement was lying 160 yards (150 m) ahead of the platoon, and had been mortally wounded while going to assist a wounded PF soldier. Thomas had tried to reach Clement and had in turn been wounded and was lying in the open between Clement and the platoon, which had pulled back. Badcoe observed that the enemy were dug in along a small rise, and appeared to be in about company-strength and readying for an attack. He gathered the PF platoon and led a frontal assault on the enemy position, firing as he went. Dodging automatic fire, he charged a machine-gun position and shot the crew with his rifle. Led by Badcoe, the PF platoon inflicted heavy casualties on the enemy. Once the PF platoon had consolidated its position, Badcoe went back, still under fire, to lift Clement and carry him out of the danger area. He then returned and assisted Thomas to a position from which he could be safely evacuated. The operation concluded successfully.
Two weeks later, the sector RF reaction company was tasked to the Quảng Điền District sub-sector on 7 March in response to an attack on its district headquarters by a VC force of about two battalions. Quảng Điền District headquarters was in the eponymous village, about 16 miles (25 km) northwest of Huế. Badcoe was travelling in a vehicle convoy with his deputy and another US officer, when their vehicle veered off the road into a ditch. His deputy was killed and Badcoe left the vehicle and joined the company commander as they drove towards the village. By the time Badcoe and the company arrived, the village was occupied by the VC, and they were attacking the district headquarters from three sides. Badcoe quickly formed the company up into platoons, then led them through enemy fire to a position which flanked the VC. Forming them into an extended line, he then led them in an assault across open ground against the main VC force. In the face of this attack, the VC withdrew in disarray and the garrison of the district headquarters was saved. Badcoe's intervention prevented serious losses and the capture of the district headquarters.
Badcoe became disillusioned with the war during his service in South Vietnam. He was particularly affected by an incident in February 1967 in which the ARVN regiment he was working with called in a napalm strike on a VC-occupied village, whose population was strongly supportive of the government, instead of attempting to attack and dislodge the VC. Badcoe and other advisers attempted to stop the use of napalm, but the ARVN divisional headquarters overruled them. A total of 40 civilians were killed or wounded, and Badcoe spent the next day-and-a-half arranging the removal of bodies and new accommodation for the survivors. He eventually concluded that the conflict was an "unwinnable war". On 7 April, Badcoe, who wrote frankly to his wife and children, penned a letter to them expressing his "unease and cynicism" about the conduct of the war and indicating that he wished to come home. At this time Badcoe was planning to take a short break on the Japanese island of Okinawa starting the following day, with an Australian Army friend who had been visiting him, observing operations.
When he returned from the field early in the morning of 7 April, Badcoe was told that he was required to act as sector headquarters duty officer due to the illness of another adviser. He saw his friend off to Da Nang and returned to Huế where he commenced duty, planning to join his friend once he had completed his shift. He soon became aware that an operation was going badly for an ARVN force at the hamlet of An Thuan in Hương Trà District, about 7.5 miles (12 km) north of Huế. The operation involved the elite Hac Bao (Black Panther) divisional reaction company of the 1st ARVN Division, along with a squadron of armoured personnel carriers (APCs) and two RF companies. They were attempting to eliminate a VC force of about two companies which was holding well-entrenched positions at An Thuan. The ARVN force had been met with intense fire and had suffered heavy casualties. Badcoe realised that the force did not have any advisers, because one of the Hac Bao advisers was ill, and advisers were required to work in pairs. Without any advisers, the ARVN were unable to access close air support to dislodge the VC.
Badcoe decided that he needed to go out to the ARVN force and assist them. He arranged for relief as the sector duty officer, grabbed his weapons and equipment, and collected Sergeant Alberto Alvarado, his US Army deputy adviser and radio operator. They sped in their jeep towards An Thuan. Upon arrival, they found the ARVN force preparing for another assault, which was to consist of the APCs followed by the Hac Bao company. Badcoe and his deputy climbed aboard an APC and joined the attack. About 820 feet (250 m) from An Thuan, the force was moving through the hamlet's cemetery and hostile fire increased markedly, from recoilless rifles, mortars, machine guns and small arms. The APCs drove through the cemetery and deployed to suppress the enemy fire. The Hac Bao company pressed forward through the cemetery, at which time Badcoe and Alvarado dismounted and joined them. During the last stages of the attack, the two advisers were leading the infantry when the enemy fire became so heavy that both the APCs and infantry began falling back through the cemetery.
Badcoe began rallying the ARVN soldiers to renew the assault, and artillery was called in on the enemy positions. After this, Badcoe and Alvarado again pushed forward, attempting to encourage the ARVN troops to press home the attack. The final stages of the line of assault crossed dry, open rice paddy fields with no cover. Enemy fire converged on Badcoe, Alvarado and the ARVN troops, who again went to ground. On this occasion, Badcoe refused to fall back. He headed straight for an enemy machine-gun position that was causing devastation among the ARVN force. Forced to ground by the intense fire, Badcoe was soon joined by Alvarado. Badcoe lifted himself up to throw a hand grenade, but was pulled down by Alvarado as bullets cracked overhead. When he rose to throw again, he was cut down by machine-gun fire and killed instantly. Alvarado attempted to recover his body, but was shot in the leg. He then used his radio to call in close air support and more artillery to suppress the enemy fire. The Hac Bao company, supported by the APCs, then moved forward and captured the objective.