The answer is so obvious: He was hanging up his shoe phone after talking with Siegfried.
But seriously, this is actually two questions: Why was he hammering his shoe? What was going on in the UN at the time?
I think the answer to the first question is obvious–to get attention. Why he chose that method is a mystery that may never be answered.
Now, for the answer to the second question–this is from Walter Cronkite’s “I Can Hear It Now:”
(Cronkite speaking, sound of gavel rapping)
"As Nikita Khrushchev hammered on his desk at the United Nations, Secretary General Dag Hammarskjold sat in outraged silence and the president of the assembly futilely rapped for order–one of those spectacles of disbelief that riddled the '60’s.
“At another point, Prime Minister Harold McMillan was speaking, and few remember his classic ad lib:”
(McMillan speaking with classic British dry wit, Khrushchev pounding shoe)
“I. . . I. . .I’d like it translated if you would, certainly.” (sounds of laughter)
“Hammarskjold was fighting for his job and the future of the United Nations as the Soviets attempted in October 1960 to substitute the role of the Secretary General with a three-man troika.”
“It is not the Soviet Union, or indeed, and other Big Powers who needs (the) United Nations for protection–it is all the OTHERS. I shall remain in my post during my term of office as a servant of the organization in the interests of all those other nations as long as THEY wish me to do so.”
“In a desperate mission to the Congo to stabilize the deteriorating situation there, the United Nation’s most innovative Secretary died in a plane crash. Circumstances were never fully explained.”
So there you have it. I don’t know exactly what the “deteriorating situation” was in the Congo, but I do know this:
In August, 1960, they gained independence, and the Soviets and the Americans were both jockeying for influence. The Soviets eventually won out, until they were ousted in 1967, by “our guy,” President Mobutu. He was in power until just a few years ago. It was another case of “our dictator over their dictator.”