The Mây Tào Mountains are a set of tortoise shaped mountains 45 kilometres north east of Nui Dat and was primarily located in Binh Tuy Province and partly with the Phước Tuy Province and Long Khánh Province. Nui Mây Tào was the topographical junction point for the Long Khánh, Binh Tuy and Phước Tuy provinces.
During the Vietnam War the mountains were used as a headquarters for the VC 5th Division and VC 275th Regiment, known as May Tao Secret Zone 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 assaulted the complex and constructed a fire support base (FSB Castle) upon one of the mountains, suffering 8 killed during or supporting the operation.