However, the superpowers spent another four weeks arguing over the number of assistant secretaries-general, before finally resolving their dispute by allowing Thant to decide for himself.

Secretary-General Dag Hammarskjöld had been actively engaged in the Congo Crisis, flying frequently to the war zone to supervise the U.N. peacekeeping mission.

On 18 September 1961, Hammarskjöld flew to Ndola in Northern Rhodesia to meet with rebel leader Moïse Tshombe of the State of Katanga.

[1] The airplane crash set off a succession crisis at the United Nations,[1] as Hammarskjöld's death required the Security Council to vote on a successor.

[4] U.S. Secretary of State Dean Rusk admitted on 22 September 1961 that "an immediate agreement cannot be expected" and suggested filling the secretary-generalship on a temporary basis.

[4] The Soviet Union, India, Ireland, and the Scandinavian countries argued that the Security Council must act to select a replacement for Hammarskjöld.

Nathan Barnes of Liberia, as President of the Security Council, attempted to arrange for Great Power consultations on the topic.

The Soviet Union agreed to select a single acting secretary-general, and the United States dropped Mongi Slim in favor of U Thant.

[16] The Security Council met in closed session on 3 November 1961, unanimously adopting Resolution 168 to recommend U Thant to the General Assembly.

A resolution was presented that afternoon by Ceylon, Liberia, and the United Arab Republic, all of them non-permanent members of the Security Council.

In a unanimous vote of 103-0-0, the General Assembly appointed U Thant as acting secretary-general of the United Nations for a term ending on 10 April 1963.

[19] A second term was assured when Soviet Premier Nikita Khrushchev made several favorable references to Thant in letters to U.S. President John F. Kennedy.

[20] No formal resolution was adopted by the Security Council, and Thant would henceforth consider his first five years in office to be a single term.

[24] The prospect of a smooth re-selection was clouded on 1 September 1966, when Thant released a statement saying, "I have decided not to offer myself for a second term as Secretary General.

[26] The face-saving statement came on 1 December 1966, when Thant met with the President of the Security Council and all of the permanent members except for Nationalist China.

Unlike the 1966 selection, several candidates entered the race after Thant's declaration, beginning with Max Jakobson of Finland on 20 January 1971.