was also described as a tremendous success of the Portuguese Armed Forces. Arriaga, however, was removed from his powerful military post in Mozambique by Marcelo Caetano shortly before the events in Lisbon that triggered the end of the war and the independence of the Portuguese territories in Africa. The reason for Arriaga's abrupt fate was an alleged incident with indigenous civilian populations, and the Portuguese government's suspicion that Arriaga was planning a military coup against Marcelo's administration in order to avoid the rise of leftist influences in Portugal and the loss of the African overseas provinces. The construction of the Cahora Bassa Dam tied up nearly 50 percent of the Portuguese troops in Mozambique, and brought the FRELIMO to the Tete Province, closer to some cities and more populated areas in the south. The FRELIMO failed, however, to halt the construction of the dam. In 1974, the FRELIMO launched mortar attacks against Vila Pery (now Chimoio), an important city and the first (and only) heavy populated area to be hit by the FRELIMO. In Mozambique special units were also used by the Portuguese Armed Forces: Grupos Especiais (Special Groups): locally raised counter-insurgency troops similar to those used in Angola Grupos Especiais Pára-Quedistas (Paratrooper Special Groups): units of volunteer black soldiers that were given airborne training Grupos Especiais de Pisteiros de Combate (Combat Tracking Special Groups): special units trained in tracking and locating guerrillas forces Flechas (Arrows), a special forces unit of the Portuguese secret police, formation of indigenous scouts and trackers, similar to the one employed in Angola Major counter-insurgency operations 1970 Mozambique – Gordian Knot Operation (Operação Nó Górdio) 1970 Guinea-Bissau – Operation Green Sea (Operação Mar Verde) 1971 Angola – Frente Leste (Portuguese for "Eastern Front") Role of the Organisation of African Unity The Organization of African Unity (OAU) was founded May 1963. Its basic principles were co-operation between African nations and solidarity between African peoples. Another important objective of the OAU was an end to all forms of colonialism in Africa. This became the major objective of the organization in its first years and soon OAU pressure led to the situation in the Portuguese colonies being brought up at the UN Security Council. The OAU established a committee based in Dar es Salaam, with representatives from Ethiopia, Algeria, Uganda, Egypt, Tanzania, Zaire, Guinea, Senegal, Nigeria, to support African liberation movements. The support provided by the committee included