In September 1961 , United Nations Secretary-General Dag Hammarskjöld was killed in a plane crash en route to Congo . The Security Council hurriedly searched for a new Secretary-General , but over the next few weeks it was in a deadlock , with the United States and the Soviet Union unable to agree on any candidate proposed by other members . The superpowers backed down when representatives from smaller nations and the Non-Aligned Movement proposed Thant to fill Hammarskjöld 's unexpired term . On 3 November 1961 , Thant was unanimously appointed as acting Secretary-General by the General Assembly , on the recommendation of the Security Council in Resolution 168 . On 30 November 1961 , the General Assembly unanimously appointed him secretary-general for a term of office ending on 3 November 1966 . During his first term , he was widely credited for his role in defusing the Cuban Missile Crisis and for ending the civil war in the Congo . He also said that he wanted to ease tensions between major powers while serving at the UN
in a plane crash
1961 Ndola United Nations DC-6 crash
U Thant