Portugal responded by embarking on a massive buildup of military personnel and security forces in Mozambique. It also established close defence ties with two of Mozambique's neighbours, Rhodesia and South Africa. In 1970, the Portuguese launched Operation Gordian Knot, which was initially successful at eliminating large numbers of FRELIMO guerrillas and their support bases in the north of the country; however, the redeployment of so many Portuguese troops to northern Mozambique allowed FRELIMO to intensify its operations elsewhere in the country. The following year, Portugal established an informal military alliance with Rhodesia and South Africa known as the Alcora Exercise. Representatives from the defence establishments of the three countries agreed to meet periodically to share intelligence and coordinate operations against militant nationalist movements in their respective countries. Simultaneously, FRELIMO also pursued close relations with the latter; for example, by 1971 it had cultivated an alliance with the Zimbabwe African National Liberation Army (ZANLA). ZANLA insurgents were permitted to infiltrate Rhodesia from FRELIMO-held territory. During the late 1960s, the Azanian People's Liberation Army (APLA) also took advantage of the gradual disintegration of Portuguese military control in Mozambique to begin infiltrating South Africa from that territory.