<P> Richard Bach wrote his book Stranger to the Ground centred around his experience as an Air National Guard pilot on this deployment . </P> <P> The four powers governing Berlin (Soviet Union, United States, United Kingdom, and France) had agreed at the 1945 Potsdam Conference that Allied personnel could move freely 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 theatre in East Berlin . The former Army General Lucius D. Clay, US President John F. Kennedy's Special Advisor in West Berlin, decided to demonstrate American resolve . </P> <P> Clay sent an American diplomat, Albert Hemsing, to probe the border . While probing in a vehicle clearly identified as belonging to a member of the US Mission in Berlin, Hemsing was stopped by East German 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--British cars were not immediately recognisable as belonging to the staff in Berlin--was stopped the next day and showed his identity card identifying him as a member of the British Military Government in Berlin, infuriating Clay . </P> <P> US Commandant General Watson was outraged by the East Berlin police's attempt to control the passage of American military forces . He communicated to the Department of State on 25 October 1961 that Soviet Commandant Colonel Solovyev and his men were not doing their part to avoid disturbing actions during a time of peace negotiations, and demanded that the Soviet authorities take immediate steps to remedy the situation . Solovyev replied by describing American attempts to send armed soldiers across the checkpoint and keeping American tanks at sector boundary as an "open provocation" and a direct violation of GDR regulations . He insisted that properly identified American military could cross the sector border without impediments, and were only stopped when their nationality was not immediately clear to guards . Solovyev contended that requesting identifying paperwork from those crossing the border was not unreasonable control; Watson disagreed . In regards to the American military presence on the border, Solovyev warned: </P>

The berlin crisis precipitated the building of the berlin wall by the soviet union