powers: the USA, UK, France and Soviet Russia and supervised by an Allied Commission. The four-power occupation of Vienna differed in one key respect from that of Berlin: the central area of the city, known as the first district, constituted an international zone in which the four powers alternated control on a monthly basis. The control was policed by the four powers on a defacto day to day basis..the famous "four soldiers in a jeep" method. The Berlin Blockade of 1948 raised allied concerns that the Russians might repeat the blockade in Vienna. The matter was raised in the UK House of Commons, There was a lack of airfields in the Western sectors, and authorities drafted contingency plans to deal with such a blockade. Plans included the laying down of metal landing mats at Schönbrunn. The Soviets did not embark on a wholesale blockade of the city. Some historians have argued that the Potsdam Agreement included written rights of land access to the western sectors, whereas no such written guarantees had covered the western sectors of Berlin. During the 10 years of the four-power occupation, Vienna became a hot-bed for international espionage between the Western and Eastern blocs. In the wake of the Berlin Blockade, the Cold War in Vienna took on a different dynamic. While accepting that Germany and Berlin would be divided, the Russians had decided against allowing the same state of affairs to arise in Austria and Vienna.
They put up barbed wire fences around the perimeter of West Berlin in 1953, but not in Vienna. By 1955, the Russians agreed to relinquish their occupation zones in Eastern Austria, and East Vienna, as well as their sector in the fourth and tenth districts in South Vienna. In exchange they required a permanent neutrality clause to be enshrined into the new Austrian State Treaty - thus ensuring that Austria would not be a member of NATO and that NATO forces would therefore not have direct communications between Italy and West Germany. In 1955,
