The Battle of Long Tan (18–21 August 1966) took place in a rubber plantation near Long Tân, in Phước Tuy Province, South Vietnam, during the Vietnam War. The action was fought between Viet Cong (VC) and People's Army of Vietnam (PAVN) units on one side and elements of the 1st Australian Task Force (1 ATF) on the other.
Australian signals intelligence (SIGINT) had tracked the VC 275th Regiment and D445 Battalion moving to a position just north of Long Tan. By 16 August, it was positioned near Long Tan outside the range of the one ATF artillery at Nui Dat. Using mortars and recoilless rifles (RCLs), on the night of 16–17 August, the VC attacked Nui Dat from a position 2 kilometres (1.2 mi) to the east, until counter-battery fire made it stop. The next morning D Company, 6th Battalion, Royal Australian Regiment (6 RAR), departed Nui Dat to locate the firing positions and determine the direction of the VC withdrawal. D Company found weapon pits and firing positions for mortars and RCLs, and around midday on 18 August made contact with VC elements.
Facing a larger force, D Company called in artillery support. Heavy fighting ensued as the VC attempted to encircle and destroy the Australians, who were resupplied several hours later by two UH-1B Iroquois from No. 9 Squadron RAAF. With the help of strong artillery fire, D Company held off a regimental assault before a relief force of M113 armoured personnel carriers and infantry from Nui Dat reinforced them that night. Australian forces then pulled back to evacuate their casualties and formed a defensive position; when they swept through the area next day, the VC had withdrawn and the operation ended on 21 August.
Although one ATF initially viewed Long Tan as a defeat, the action was later re-assessed as a strategic victory since it prevented the VC moving against Nui Dat. The VC also considered it a victory, due to the political success of an effective ambush and securing of the area around the village. Whether the battle impaired the capabilities of the VC is disputed.
The 1st Australian Task Force (1 ATF) began arriving in Phước Tuy Province of South Vietnam between April and June 1966. Following the establishment of its base at Nui Dat in Operation Hardihood, platoon patrols and ambushes were initially conducted out to Line Alpha (4,000 metres (4,400 yd)), which was the range of the Viet Cong (VC) mortars, but were later extended out to Line Bravo (10,000 metres (11,000 yd)) to counter the threat from artillery.
All inhabitants of Long Phước and Long Hải villages within Line Alpha were resettled nearby. A protective security zone was established and a free-fire zone declared. Although unusual for allied installations in Vietnam, many of which were located near populated areas, the Australians hoped to deny the VC observation of Nui Dat, and afford greater security to patrols. While adding to the physical security of the base through disrupting a major VC support area and removing the local population from danger, such measures may have been counter-productive. The resettlement resulted in widespread resentment.
The VC continued to observe the base from the Nui Dinh hills. On 10 June reports indicated that a VC regiment was moving towards Nui Dat from the north west and was about 10 kilometres (6.2 mi) away. The same day three 120 mm mortar rounds landed just outside the base. That night Australian artillery fired on suspected movement along Route 2, but no casualties were found the next day. Further warnings of an attack hastened the call-forward of 6th Battalion, Royal Australian Regiment (6 RAR), which arrived from Vũng Tàu 30 kilometres (19 mi) to the south on 14 June. No attack occurred, and the initial reaction to 1 ATF's lodgement proved unexpectedly limited.
The principal communist units in Phước Tuy were main forces from the 274th and 275th Regiments of the VC 5th Division. Under command of Senior Colonel Nguyen The Truyen, the division was headquartered in the Mây Tào Mountains. Operating in Phước Tuy, Biên Hòa and Long Khánh Provinces, it comprised both South Vietnamese VC guerrillas and North Vietnamese People's Army of Vietnam (PAVN) units. Given the task of isolating the eastern provinces from Saigon by interdicting the main roads and highways, including National Routes 1 and 15 and provincial routes 2 and 23, it proved a major challenge to Army of the Republic of Vietnam (ARVN) units that ventured into the province, demonstrating a capacity to mount regimental-size ambushes. The 274th Regiment was the stronger and better trained of the two. Based in the Hát Dịch in north west Phước Tuy with three battalions—D800, D265 and D308—it numbered 2,000 men. The 275th Regiment was based in the Mây Tào Mountains and mainly operated in the east of the province. Commanded by Senior Captain Nguyen Thoi Bung (aka Ut Thoi), it consisted of three battalions—H421, H422 and H421—with a total of 1,850 men.
In support was an artillery battalion equipped with 75 mm recoilless rifles (RCLs), 82 mm mortars, and 12.7 mm heavy machine-guns, an engineer battalion, a signals battalion and a sapper reconnaissance battalion, as well as medical and logistic units. Local forces included D445 Battalion, which normally operated in the south and in Long Khánh. Under command of Bui Quang Chanh (alias Sau Chanh), it consisted of three rifle companies—C1, C2, C3—and a weapons company, C4; a strength of 550 men. Recruited locally and operating in familiar terrain, they possessed an intimate knowledge of the area. Guerrilla forces numbered 400, operating in groups of five to 60, with two companies in Châu Đốc district, one in Long Dat, and a platoon in Xuyên Mộc. In total, VC strength was estimated to have been around 4,500 men.
ARVN forces included the 52nd Ranger Battalion, a unit that had previously earned a US Presidential Unit Citation defeating the 275th Regiment the year before, and relatively weak territorial forces of 17 Regional Force (RF) companies and 47 Popular Force (PF) platoons, in total some 4,500 men. Most villages were garrisoned by an RF company operating from a fortified compound, and PF platoons guarded most hamlets and important infrastructure, but their value was questionable. RF companies were technically available for tasks throughout the province, while PF platoons were mostly restricted to operating around their village. While RF and PF units occasionally defended themselves successfully they rarely conducted offensive operations, and when they did they were usually limited. Mostly recruited from the same population as their opponents, they often suffered equally at the hands of the VC and a largely inept government. Poorly trained and unable to rely on being reinforced, they provided little opposition to the VC. A US Advisory Team operated in support, as did a few Australians from the Australian Army Training Team Vietnam (AATTV); despite their efforts, the capabilities of the ARVN remained limited. The arrival of 1 ATF further restricted their ability to operate in Phước Tuy as it increasingly came to dominate the province.
Initially, 1 ATF, under the command of Brigadier Oliver David Jackson, consisted of two infantry battalions: the 5th Battalion, Royal Australian Regiment (5 RAR), commanded by Lieutenant Colonel John Warr, and 6 RAR under Lieutenant Colonel Colin Townsend. Other units included the 1st Armoured Personnel Carrier Squadron operating M113 armoured personnel carriers (APCs); 1st Field Regiment, Royal Australian Artillery, consisting of the New Zealand 161st Battery, two Australian batteries equipped with eighteen 105 mm L5 Pack Howitzers, and six 155 mm M109 self-propelled howitzers from the US A Battery, 2nd Battalion, 35th Artillery Regiment; 3rd SAS Squadron; 1st Field Squadron and 21st Engineer Support Troop; 103rd Signals Squadron; 161st Reconnaissance Flight operating Cessna 180s and Bell H-13 Sioux light observation helicopters; and an intelligence detachment. Support was provided by the 1st Australian Logistic Support Group (1 ALSG) at Vũng Tàu, and eight UH-1B Iroquois helicopters from No. 9 Squadron RAAF. US forces provided considerable support including artillery, close air support, helicopter gunships, and utility, medium and heavy lift helicopters. The largest Australian force deployed since the Second World War, it had been rapidly assembled. Although many of its officers and non-commissioned personnel had extensive operational experience, it included many National Servicemen. Few had direct experience of counter-insurgency operations, or first-hand understanding of the situation in Vietnam. The task force was unable to train together before departure.