On 17 September 1961 , UN Secretary General Dag Hammarskjöld was flying to Rhodesia to negotiate peace talks between the government and Tshombe when Hammarskjöld 's plane crashed , killing him . It was a response to the troubled Operation Morthor ongoing at the time . The circumstances of his death were suspicious , and there remains suspicion that his plane was shot down . A recent book by Susan Williams ( 2011 ) uncovered evidence that a specially equipped fighter plane from the Belgian-led mercenary force referred to as the Katanga Gendarmerie shot down his plane . Hammarskjöld was replaced by U Thant
when Hammarskjöld 's plane crashed
1961 Ndola United Nations DC-6 crash
United Nations Operation in the Congo