Operation Grandslam was an offensive undertaken by United Nations peacekeeping forces from 28 December 1962 to 15 January 1963 against the forces of the State of Katanga, a secessionist state rebelling against the Republic of the Congo in central Africa. The Katangese forces were decisively defeated and Katanga was forcibly reintegrated into the Congo.
The United Nations had tried several times to reconcile the government of the Congo with the State of Katanga, which had declared independence under Moïse Tshombe with Belgian support in 1960. Though initially limiting its actions, the United Nations Operation in the Congo became increasingly impatient towards Katanga and Tshombe, drawing up plans to resolve the situation through force. Tshombe continuously violated agreements he had made with the United Nations and the Congolese government by building up his forces and bringing foreign mercenaries into the conflict. The situation reached a breaking point in December 1962 when Katangese gendarmes attacked peacekeeping forces in Katanga. United Nations Secretary-General U Thant authorised a retaliatory offensive to eliminate secessionist opposition.
Reinforced by aircraft from Sweden, United Nations peacekeepers completed the first phase of the operation, securing the Katangese capital, Élisabethville and destroying much of the Katangese Air Force by the end of the year. In early January, the United Nations forces turned their attention towards remaining strongholds in southern Katanga. Indian peacekeepers exceeded their orders and crossed the Lufira River ahead of schedule, generating panic behind the Katangese lines and embarrassing the United Nations leadership. Tshombe, realising that his position was untenable, approached Thant for peace. On 17 January 1963, he signed an instrument of surrender and declared the Katangese secession to be over. The central government reorganised the provincial administration of Katanga to weaken its political structure. Tshombe initially participated but feared his arrest and fled to Europe.
Many Katangese gendarmes and their mercenary leaders took refuge in Angola to reorganise, acting under orders from Tshombe. In 1964, Tshombe was welcomed back to the Congo and made Prime Minister. He immediately called on his forces to suppress communist revolts in the east and centre of the country. This they accomplished but Tshombe was dismissed from his post in 1965, ultimately losing all contact with them following his imprisonment in Algeria in 1967. Relations between the new central government and the gendarmes soured and, after a mutiny was repressed, they returned to Angola. An insurgency for Katangese secession continues to the present day.
Background
Katanga's secession
Following the Republic of the Congo's independence from Belgium in 1960, the country fell into disorder as the army mutinied. Shortly thereafter South Kasai and the State of Katanga declared independence from the Congolese government. The latter contained the vast majority of the Congo's valuable mineral resources and attracted significant mining activity under Belgian rule. Many Katangese thought that they were entitled to the revenue generated through the lucrative industry, and feared that under the new central government it would be distributed among the Congo's poorer provinces. Resulting nativist politics with support from the Belgian government and private interests such as the Union Minière du Haut Katanga (UMHK) precipitated the Katangese secession.
The deposition—and eventual murder—of Prime Minister Patrice Lumumba caused further issues in the country, leading to the declaration of a rival government in Stanleyville by the end of the year. To prevent a complete collapse of order within the country, the United Nations established a major peacekeeping mission, the United Nations Operation in the Congo (known under its French acronym as ONUC). In addition to a large body of troops (20,000 at its peak strength), a civilian mission was brought in to provide technical assistance to the Congolese government. Initially, ONUC limited its actions to ensuring the safety of Congolese citizens and foreign nationals and refrained from acting against the secessionist states, but the UN ran into trouble in Katanga. The state's leader and head of the locally entrenched Confédération des associations tribales du Katanga (CONAKAT), Moïse Tshombe, at first banned the UN from entering his territory and then greatly limited their peacekeeping efforts. Further issues derived from peacekeepers' attempts to deport foreign mercenaries, many of whom were employed by Katanga.