By mid-1971, Vietnamization was hollowing out the allied war effort. The Australian government, eager to reduce its commitment, had declined to replace the 8th Battalion when it rotated home in December 1970. The 1st Australian Task Force was down to two infantry battalions covering the same vast area of operations -- a burden that grew heavier with each departure. Yet the preceding years had not been wasted. A sustained campaign in Phuoc Tuy Province between 1969 and 1970 had driven the major VC and PAVN formations out to recuperate, and by late 1970 the Army of the Republic of Vietnam was increasingly responsible for the security of population centres. The days of large set-piece battles seemed over. Then, in May 1971, Brigadier Bruce McDonald extended the Australian area of operations four kilometres north into Long Khanh Province, and Special Air Service patrols promptly detected a substantial enemy force using the area to rest, retrain, and refit.

Intelligence located the VC D445 Battalion and the PAVN 3/33 Regiment east of Route 2, thirty kilometres north of the Australian base at Nui Dat. McDonald's plan was a classic hammer-and-anvil: blocking forces of Australian, New Zealand, and American troops along the Suoi Ran river, with 3 RAR under Lieutenant Colonel Peter Scott and Centurion tanks from C Squadron, 1st Armoured Regiment driving the enemy into them. On 5 June, 3 RAR was inserted by helicopter into a landing zone barely five hundred metres from an extensive bunker system nobody knew was there. As the first company touched down, intense fire erupted from the treeline. It slackened after a few minutes -- long enough to get the remaining companies on the ground -- but the Australians were already patrolling inside the enemy's perimeter. Signs of a strong presence appeared immediately: fresh tracks, abandoned equipment, small parties observed moving north.

Late on 6 June, 5 Platoon of B Company found what appeared to be the main enemy position. With nightfall approaching, the attack was postponed. At six the next morning, after thirty minutes of artillery preparation, the platoon advanced expecting the VC to have slipped away overnight, as they had done so many times before. Ninety metres into the advance, the jungle exploded. Heavy fire from the front and both flanks cut down several Australians in the opening volleys. The platoon was pinned on the edge of a well-concealed bunker system, and the platoon commander called for helicopter gunships and mortar fire rather than risk further casualties in a withdrawal. For hours, 5 Platoon held on while their M60 machine guns began failing from sustained firing and ammunition ran dangerously low. VC fighters emerged from their bunkers to outflank the Australians, and only massed indirect fire and helicopter gunship runs prevented them from being overrun. Lieutenant Ian Mathers, the forward observer, moved up to direct fire support and was killed almost immediately.

By mid-morning, the rest of B Company had linked up with the beleaguered platoon and stabilized the line. At 11:00, a resupply helicopter was shot down by heavy ground fire and exploded on impact, killing two crew members. Ammunition cooked off in the burning wreckage as Australians scrambled through the debris to pull survivors clear. The situation demanded armour. D Company mounted in APCs with Centurion tanks spearheading the assault pushed into the bunker complex from the northeast. The tanks crushed bunkers and their occupants beneath their tracks as resistance gradually slackened. But the position was enormous -- nearly a square kilometre of interconnected fighting positions, wider than D Company's entire assault front. The Australians searched each bunker methodically while C Company, to the south, uncovered and captured a second system that had been hastily abandoned. The ammunition expenditure told the story: over 16,000 rounds of M60 fire, 6,000 rounds of M16, more than 1,400 rounds of 105mm and 200 rounds of 155mm artillery.

Operation Overlord cost the Australians ten killed and twenty-four wounded across the full operation. Only five VC bodies were recovered in the initial battle, though blood trails and remains in crushed bunkers indicated far heavier casualties. The grim arithmetic obscured a tactical reality: the VC had defended hard enough to evacuate their personnel and stores, and the Australians had lacked the combat power to seal the trap. Six days later, the VC 274th Regiment proved the point by ambushing an Australian headquarters platoon, killing seven soldiers when a rocket-propelled grenade detonated a crate of Claymore mines atop an armoured personnel carrier. Overlord ended on 14 June, and 1 ATF returned to Nui Dat. It was one of the largest Australian task force operations of the war and the last joint US-Australian battalion-sized operation in Vietnam. Two months later, Prime Minister William McMahon announced the beginning of Australia's withdrawal. By 1973, the last Australian forces had left South Vietnam. The jungle of Long Khanh Province, cratered and churned, slowly reclaimed the bunkers.