Operation Unokat, also styled Operation UNOKAT, was an offensive undertaken by United Nations peacekeeping forces from 5 to 21 December 1961 against the gendarmerie of the State of Katanga, a secessionist state rebelling against the Republic of the Congo (now the Democratic Republic of the Congo) in Central Africa. 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.

Following the failure of Operation Morthor and the death of Secretary-General of the United Nations Dag Hammarskjöld in a plane crash, the new Secretary-General U Thant, backed by renewed international support, called for a more robust peacekeeping approach and for the UN to take more military action. A number of skirmishes between Katangese troops and UN forces in the Katangese capital of Élisabethville, and the establishment of roadblocks by the Katangese, led to the UN launching Operation Unokat.

The Katangese forces were gradually pushed back and UN forces secured Élisabethville. The Katangese agreed to negotiate an agreement with the Congolese central government, which led to the Kitona Declaration stating that Katanga was part of the Congo and planned to re-integrate with the Congo. However, the agreement was not carried out, forcing the UN to launch Operation Grandslam to forcibly reintegrate Katanga and end the secession.

Following the Republic of the Congo's independence from Belgium in 1960 after over 50 years of colonial rule, 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 felt 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.

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 sent to provide technical assistance to the Congolese government. A new Congolese coalition government was formed in Léopoldville under Prime Minister Cyrille Adoula in August 1961. It faced great pressure to reintegrate Katanga into the Congo and risked collapse if this was not achieved, something ONUC was keen to avoid. The United States also desired reintegration for this end, fearing Adoula's removal would result in his replacement by left-wing politician Antoine Gizenga and allow the Soviet Union to gain influence in the country.

The UN Security Council passed a resolution permitting ONUC to use military force to prevent civil war, make arrests, halt military operations, arrange ceasefires, and deport foreign military personnel. Under the authorisation of this resolution, UN forces launched Operation Rum Punch and Operation Morthor with the aim of securing their own positions in Katanga and eliminating the presence of mercenaries in Élisabethville, the Katangese capital. The former, though limited in scope, was largely successful, but the latter failed to achieve its objectives. As Morthor was underway, Special Representative Conor Cruise O'Brien announced, "The secession of Katanga has ended." This statement was quickly realised to be premature; Katanga fought the offensive to a stalemate.

United Nations Secretary-General Dag Hammarskjöld attempted to meet Tshombe for negotiations in Northern Rhodesia, but on the night of 17 September his plane crashed, killing all aboard. Hammarskjöld's untimely death, combined with an overall rise in tensions, helped rally international support for a more robust peacekeeping approach. His replacement, U Thant, was less averse to using military force in the Congo and believed that the UN should intervene in internal Congolese affairs. Thant promptly requested that the Security Council grant ONUC a stronger mandate. This came in the form of a resolution on 24 November, which maintained the goals of previous ONUC resolutions and cleared up any remaining ambiguities surrounding the role and nature of the UN's intervention. It reaffirmed ONUC's ability to detain and deport foreign military personnel and mercenaries with force, described Katanga's secessionist activities as illegal, and declared the UN's support for the central government of the Congo in its efforts to "maintain law and order and national integrity". Tshombe immediately responded to the resolution by broadcasting an inflammatory speech against ONUC. ONUC's command structure in Katanga, mindful of the new mandate, issued instructions to UN troops to put "an end to Katangese resistance to UN policy by destruction of Gendarmerie and other anti-UN resistance".

On 28 November 1961 members of the Katangese Gendarmerie assaulted the UN Representative in Katanga George Ivan Smith and diplomat Brian Urquhart as they travelled to a diplomatic function. Smith was allowed to leave, but the gendarmes held Urquhart overnight. ONUC subsequently sent out teams to search for him, and its Katanga-based command structure issued an order to respond to such incidents with "hard hitting swiftness. ... Such measures entail hitting at gendarmerie. ... We must have sufficient strength NOT only to hit such concentrations but to take all the consequences of such actions such as meeting counter attacks at various points and putting down ruthlessly European mercenaries and volunteer elements." Tshombe secured Urquhart's release after the UN threatened to attack his presidential palace.