Portugal's sudden retreat from Angola and Mozambique in 1975 ended a history of South African military and intelligence cooperation with Portugal against the Angolan and Namibian liberation movements dating back to the 1960s.It also ended economic cooperation with regard to the Cunene hydro-project at the Angolan-Namibian border, which South Africa had financed.
South African involvement in Angola, subsumed under what it called the South African Border War, started in 1966 when the conflict with the Namibian independence movement, SWAPO, which at that time had its bases in Ovamboland and Zambia, first flared up. With the loss of the Portuguese as an ally and the establishment of pro-SWAPO communist rule in the two former colonies the apartheidregime lost highly valued sections of its "cordon sanitaire" (buffer zone) between itself and hostile black Africa. In the following years South Africa engaged in numerous military and economic activities in the region, backing RENAMO in the Mozambican Civil War, undertaking various measures at economic destabilization against Botswana, Lesotho, Malawi, Mozambique, Swaziland,Tanzania, Zambia and Zimbabwe, backing an unsuccessful mercenary intervention in the Seychelles in 1981 and supporting a coup in Lesotho in 1986. It was behind a coup attempt in Tanzania in 1983, provided support for rebels in Zimbabwe since independence, carried out raids against ANC offices in Maputo, Harare and Gaborone and conducted a counterinsurgency war in Namibia against SWAPO. SWAPO retreated to and operated from bases in Angola and South Africa was confronted not only with the issue of having to cross another border in pursuit of SWAPO but also of another leftist government in the region. Unlike the other countries in the region, South Africa had no economic leverage on Angola, thus making military action the only possible means to exert any influence on the course of events.
On 14 July 1975 South African Prime Minister Vorster approved weapons worth US $14 million to be bought secretly for FNLA and UNITA. First arms shipments for FNLA and UNITA from South Africa arrived in August 1975.
On 9 August 1975 a 30-man patrol of the South African Defence Force (SADF) moved some 50 km into southern Angola and occupied the Ruacana-Calueque hydro-electric complex and other installations on the Cunene River. Several hostile incidences with UNITA and SWAPO frightening foreign workers had delivered a welcome pretext.The defence of the Calueque dam complex in southern Angola was South Africa's justification for the first permanent deployment of regular SADF units inside Angola.
On 22 August 1975 the SADF launched operation "Sausage II", a major raid against SWAPO in southern Angola. In addition, on 4 September 1975, Vorster authorized the provision of limited military training, advice and logistical support. In turn FNLA and UNITA would help the South Africans fighting SWAPO. Due to the recent MPLA's successes, UNITA's territory had been shrinking to parts of central Angola, and it became clear to South Africa that independence day would find the MPLA in control of Luanda; "neither the United States nor South Africa were willing to accept that." The SADF set up a training camp near Silva Porto and prepared the defences of Nova Lisboa (Huambo). They assembled the mobile attack unit "Foxbat" to stop approaching FAPLA-units with which it clashed on 5 October, thus saving Nova Lisboa for UNITA.
On 14 October, the South Africans secretly launched Operation Savannah when Task Force Zulu, the first of several South African columns, crossed from Namibia into Cuando Cubango. Southern Angola was in chaos with the three liberation movements fighting each other for dominance. It took FAPLA some time, before it noticed who else it was up against and the SADF advanced very quickly. Task force Foxbat joined the invasion in mid-October. The operation provided for elimination of the MPLA from the southern border area, then from south western Angola, from the central region, and finally for the capture of Luanda.
"Pretoria believed that by invading Angola it could install its proxies and shore up apartheid for the foreseeable future" The United States encouraged the South Africans, had known of their covert plans in advance and co-operated militarily with its forces, contrary to Kissinger's testimony to Congress at the time, as well as at odds with the version in his memoirs and in contrast to what President Ford told the Chinese, who supported the FNLA but were worried about South African engagement in Angola. According to John Stockwell, a former CIA officer, "there was close liaison between the CIA and the South Africans" and "'high officials' in Pretoria claimed that their intervention in Angola had been based on an 'understanding' with the United States".