In 1982, landlocked Zimbabwe directly intervened in the civil war in order to secure its vital transport routes in Mozambique, stop cross-border RENAMO raids, and help its old ally FRELIMO. Zimbabwe's help became crucial to the defence of the corridors, particularly the important Beira corridor. Later Zimbabwe became engaged further, carrying out several joint operations with FRELIMO against RENAMO strongholds. Thus RENAMO had to give up its base camps in the Gorongosa area. Tanzania also sent troops to back FRELIMO. North Korea, the German Democratic Republic and the Soviet Union also armed and trained FRELIMO forces, with the North Koreans establishing a Military Mission in Mozambique during the early 1980s North Korean advisers were instrumental in the formation of FRELIMO's first specialized counter-insurgency brigade, which was deployed from 1983 onward. and the GDR providing military assistance and training members of the Mozambican FPLM in the GDR.