The Mây Tào Mountains are a set of tortoise shaped mountains 45 kilometres north east of Nui Dat

Nui Dat

Nui Dat in Phuoc Tuy Province was the location of a prominent Australian military base in South Vietnam during the Vietnam War. The site was chosen by Lieutenant General John Wilton in 1966 and was built mainly by men from the 6th Battalion, Royal Australian Regiment...

 and was primarily located in Binh Tuy Province

Binh Tuy Province

Binh Tuy Province was a province of South Vietnam. It now mostly corresponds to the western part of Binh Thuan Province, including Hàm Tân, Hàm Thuận Nam, Tánh Linh, Đức Linh districts and La Gi town....

 and partly with the Phước Tuy Province

Phuoc Tuy Province

Phước Tuy Province was a province of South Vietnam. It now mostly corresponds to Ba Ria-Vung Tau Province, just southeast of Ho Chi Minh City....

 and Long Khánh Province

Long Khánh Province

Long Khánh is former province in Dong Nam Bo region of South Vietnam. It was formed on October 22, 1956 by separating from Biên Hòa Province.On April 24, 1957, it had two districts Xuân Lộc and Định Quán.On April 30, 1975, the province was renamed to Xuan Loc....

. Nui Mây Tào was the topographical junction point for the Long Khánh, Binh Tuy and Phước Tuy provinces.

During the Vietnam War

Vietnam War

The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 the mountains were used as a headquarters for the VC 5th Division

VC 5th Division

The 5th Infantry Division, was a division of the Viet Cong during the Vietnam War. The division consisted of the 274 Regiment and 275 Regiment plus supporting units. North Vietnamese regulars also reinforced the division during operations...

 and VC 275th Regiment

VC 275th Regiment

The VC 275th Regiment, also known as the 275 Viet Cong Main Force Regiment, was a regiment of the Viet Cong during the Vietnam War. The regiment was part of the VC Division 5 and operated in the Phước Tuy province....

, known as May Tao Secret Zone

May Tao Secret Zone

The May Tao Secret Zone was a geographical area of the Republic of Vietnam—a mountainous area south east of Saigon, believed to harbour an National Liberation Front divisional sanctuary, by US military forces and news media in 1966. It was the site of numerous US military operations during the US...

 and Base Area 300, and was a well-developed, heavily dug-in, tunnelled and fortified base area. It had been an NVA HQ and logistics base, training area and hospital zone for many years. As part of Operation Marsden between 1–28 December 1969, the 6th Battalion, Royal Australian Regiment

6th Battalion, Royal Australian Regiment

6th Battalion, Royal Australian Regiment is a motorised infantry battalion of the Australian Army. It was originally raised in Brisbane, Queensland, on 6 June 1965 and has since then served in a number of overseas deployments and conflicts including South Vietnam, East Timor and Iraq...

assaulted the complex and constructed a fire support base (FSB Castle) upon one of the mountains, suffering 8 killed during or supporting the operation.