The East German government also sought a way to stop its "brain drain" as its population fled west through Berlin, made possible by the city's four-power status and the allowance of free travel.

No agreement was reached and in August 1961, with Khrushchev's backing, East German leader Walter Ulbricht ordered the closing of the border and the construction of a wall around West Berlin.

[1] In the growing confrontation over the status of Berlin, Kennedy undercut his own bargaining position during his Vienna summit negotiations with Khrushchev in June 1961.

He reiterated that the United States was not looking for a fight and that he recognized the "Soviet Union's historical concerns about their security in central and eastern Europe."

Walter Ulbricht, First Secretary of the Socialist Unity Party (SED) and Staatsrat chairman and thus East Germany's chief decision-maker, convinced the Soviet Union that force was necessary to stop this movement, although Berlin's four-power status required the allowance of free travel between zones and forbade the presence of German troops in Berlin.

[5] On 15 June 1961, two months before the construction of the Berlin Wall started, Walter Ulbricht stated in an international press conference: "Niemand hat die Absicht, eine Mauer zu errichten!"

These showed that US Secretary of State Dean Rusk, unlike the West Germans, supported talks with the Soviet Union, though the KGB and the GRU warned that the US was being pressured by other members of the alliance to consider economic sanctions against East Germany and other socialist countries and to move faster on plans for conventional and nuclear armament of their allies in Western Europe, such as the West German Bundeswehr.

At a weekly meeting of the Berlin Watch Committee on 9 August 1961, the Chief of the US Military Liaison Mission to the Commander Group of Soviet Forces Germany predicted the construction of a wall.

[1] On August 18, 1961, Chancellor Konrad Adenauer issued a statement to the Bundestag denouncing the construction of the wall by East German authorities.

[12] On 30 August 1961, in response to moves by the Soviet Union to cut off access to Berlin, President Kennedy ordered 148,000 Guardsmen and Reservists to active duty.

Most of the mobilised Air Guardsmen remained in the US, while some others had been trained for delivery of tactical nuclear weapons and had to be retrained in Europe for conventional operations.

[1] Richard Bach wrote his book Stranger to the Ground centred around his experience as an Air National Guard pilot on this deployment.

[13] President John F. Kennedy worked closely with retired Army General Lucius D. Clay, who had been in charge of the Berlin Airlift of 1948–1949.

US Commandant General Watson was outraged by the East Berlin police's attempt to control the passage of American military forces.

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.

Clay was convinced that having US tanks use bulldozer mounts to knock down parts of the Wall would have ended the crisis to the greater advantage of the US and its allies without eliciting a Soviet military response.

Frederick Kempe argues that Rusk's views support a more unfavorable assessment of Kennedy's decisions during the crisis and his willingness to accept the Wall as the best solution.

According to Cowan, the device was [eventually] retired, in part, because "it was essentially a platoon weapon," and there was apparently "great fear that some sergeant would start a nuclear war.

Also, Secretary of Defense Robert McNamara wanted to rush 171 Crocketts to USAREUR in December 1971 [dubious – discuss] [from page 224 of Marc Trachtenberg's book, HISTORY & STRATEGY (Princeton University Press, 1991)].

With GRU spy Georgi Bolshakov serving as the primary channel of communication, Khrushchev and Kennedy agreed to reduce tensions by withdrawing the tanks.