The GC-45 work was paid for by the South Africans, but it has been claimed that Bull did the work largely at the urging of the United States Central Intelligence Agency (CIA) who considered South Africa as a defence against Soviet operations in Angola. Used in South Africa as the G5 howitzer, the new guns were used near the Angolan border in 1986 when South Africa invaded the former Portuguese colony of Angola, in order to assist UNITA. Because the Marxist government of Angola was aided by Cuban troops and Soviet artillery, it was also suggested that the CIA had encouraged the South Africans to invade the country in 1975 at the beginning of the Angolan Civil War. The G5 howitzers were instrumental in securing success in Angola, although wider strategic considerations led to South Africa's eventual withdrawal.