The Berlin Crisis of 1961 (4 June -- 9 November 1961) was the last major politico-military European incident of the Cold War about the occupational status of the German capital city, Berlin, and of post--World War II Germany. The U.S.S.R. provoked the Berlin Crisis with an ultimatum demanding the withdrawal of Western armed forces from West Berlin â€” culminating with the city's de facto partition with the East German erection of the Berlin Wall. The 22nd Congress of the Communist Party of the Soviet Union â€” the last to be attended by the Communist Party of China â€” was held in Moscow during the crisis. The four powers governing Berlin (France, the Soviet Union, the United Kingdom, and the United States) had agreed at the 1945 Potsdam Conference that Allied personnel would not be stopped by German police in any sector of Berlin. But on 22 October 1961, just two months after the construction of the Wall, the US Chief of Mission in West Berlin, E. Allan Lightner, was stopped in his car (which had occupation forces license plates) while crossing at Checkpoint Charlie to go to a theater in East Berlin. The former Army General Lucius D. Clay, U.S. President John F. Kennedy's Special Advisor in West Berlin, decided to demonstrate American resolve. Clay sent an American diplomat, Albert Hemsing, to probe the border. While probing in a diplomatic vehicle, Hemsing was stopped by East German transport police asking to see his passport. Once his identity became clear, US Military Police were rushed in. The Military Police escorted the diplomatic car as it drove into East Berlin and the shocked GDR police got out of the way. The car continued and the soldiers returned to West Berlin. A British diplomat â€” apparently either out of the loop or attempting to conciliate â€” was stopped the next day and handed over his passport, infuriating Clay. Perhaps this contributed to Hemsing's decision to make the attempt again: on 27 October 1961, Mr. Hemsing again approached the zonal boundary in a diplomatic vehicle. But Clay did not know how the Soviets would respond, so just in case, he had sent tanks with an infantry battalion to the nearby Tempelhof airfield. To everyone's relief the same routine was played out as before. The US Military Police and Jeeps went back to West Berlin, and the tanks waiting behind also went home. Immediately afterwards, 33 Soviet tanks drove to the Brandenburg Gate. Curiously, Soviet premier Nikita Khrushchev claimed in his memoirs that as he understood it, the American tanks had seen the Soviet tanks coming and retreated. Col. Jim Atwood, then Commander of the US Military Mission in West Berlin, disagreed in later statements. Ten of these tanks continued to FriedrichstraÃŸe, and stopped just 50 to 100 metres from the checkpoint on the Soviet side of the sector boundary. The US tanks turned back towards the checkpoint, stopping an equal distance from it on the American side of the boundary. From 27 October 1961 at 17:00 until 28 October 1961 at about 11:00, the respective troops faced each other. As per standing orders, both groups of tanks were loaded with live munitions. The alert levels of the US Garrison in West Berlin, then NATO, and finally the US Strategic Air Command (SAC) were raised. Both groups of tanks had orders to fire if fired upon. Khrushchev and Kennedy agreed (according to one source, via a channel established just a month before) to reduce tensions by withdrawing the tanks. The Soviet checkpoint had direct communications to General Anatoly Gribkov at the Soviet Army High Command, who in turn was on the phone to Khrushchev. The US checkpoint contained a Military Police officer on the telephone to the HQ of the US Military Mission in Berlin, which in turn was in communication with the White House. Kennedy offered to go easy over Berlin in the future in return for the Soviets removing their tanks first. The Soviets agreed. In reality Kennedy was pragmatic concerning the Wall: "It's not a very nice solution, but a wall is a hell of a lot better than a war." A Soviet tank moved about 5 metres backwards first; then an American tank followed suit. One by one the tanks withdrew. But General Bruce C. Clarke, then the Commander-in-Chief (CINC) of U.S. Army Europe (USAREUR), was said to have been concerned about Clay's conduct and Clay returned to the United States in May 1962. Gen. Clarke's assessment may have been incomplete, however: Clay's firmness had a great effect on the German population, led by West Berlin Mayor Willy Brandt and West German Chancellor Konrad Adenauer.