Berlin: Challenge to Kennedy
Source: Aide memoire from Khruschev to Kennedy, June 1961
The peace treaty will specifically record the status of West Berlin as a free city, and the Soviet Union, like the other parties to the treaty, will, of course, strictly observe it and measures will also be taken to see to it that this status is also respected by the other countries. At the same time this will also mean the liquidation of the occupation régime in West Berlin with all the consequences arising from this. In particular, the questions of using land, water and air communications across the territory of the German Democratic Republic will have to be settled not otherwise than through appropriate agreements with the German Democratic Republic. This is only natural, since control over such communications is an inalienable right of any sovereign State.
Source: Kennedy Speech in response to the Aide Memoire sent by Khruschev
The real intent of the June 4 aide memoire is that East Berlin, a part of a city under 4-Power status, would be formally absorbed into the so-called German Democratic Republic while West Berlin, even though called a “free city,” would lose the protection presently provided by the Western Powers and become subject to the will of a totalitarian regime. Its leader, Herr Ulbricht, has made clear his intention, once this so-called “peace treaty” is signed, to curb West Berlin’s communications with the free world and to suffocate the freedom it now enjoys.
Source: Strategic Air Planning and Berlin
External link (pdf document). This is a copy of the now declassified documents that show that the US was preparing for a ‘First Strike’ option if the Berlin Crisis led to inevitable military conflict.