of interdicting the infiltration of guerrillas in Northern Angola from the bordering Republic of Zaire. Later, the Navy also operated in the rivers of Eastern Angola, despite it being a remote interior region at around 1000 km distance from the Ocean. The Portuguese air assets in Angola were under the command of the 2nd Air Region of the Portuguese Air Force, with headquarters in Luanda. They included a central air base (the Air Base 9 at Luanda) and two sector air bases (the Base-Aerodrome 3 at Negage, Uíge and the Base-Aerodrome 4 at Henrique de Carvalho, Lunda). A fourth air base was being built (Base-Aerodrome 10 at Serpa Pinto, Cuando-Cubando), but it was not completed before the end of the conflict. These bases controlled a number of satellite air fields, including maneuver and alternate aerodromes. Besides these, the Air Force also could count with a number of additional airfields, including those of some of the Army garrisons, in some of which air detachments were permanently deployed. The Air Force also maintained in Angola, the Paratrooper Battalion 21, which served as a mobile intervention unit, with its forces initially being deployed by parachute, but later being mainly used in air assaults by helicopter. The Air Force was supported by the voluntary air formations, composed of civil pilots, mainly from local flying clubs, who operated light aircraft mainly in air logistics support missions. In the beginning of the conflict, the Air Force had only a few aircraft stationed in Angola, including 25 F-84G jet fighter-bombers, six PV-2 Harpoon bombers, six Nord Noratlas transport aircraft, six Alouette II helicopters, eight T-6 light attack aircraft and eight Auster light observation aircraft. By the early 1970s, it had available four F-84G, six PV-2 Harpoon, 13 Nord Noratlas, C-47 and C-57 transport aircraft, 30 Alouette III and Puma helicopters, 18 T-6 and 26 Dornier Do 27 observation aircraft. Despite the increase, the number of aircraft was always too few to cover the enormous Angolan territory, besides many being old aircraft difficult to maintain in flying conditions. From the late 1960s, the Portuguese forces in southern Angola were able to count with the support of helicopters and some other air assets of the South African Air Force, with two Portuguese-South African joint air support centers being established. Security forces The security forces in Angola were under the control of the civil authorities, headed by the Governor-General of