After the Marshall Plan, the introduction of a new currency to Western Germany to replace the debased Reichsmark and massive electoral losses for communist parties, in June 1948, the Soviet Union cut off surface road access to Berlin, initiating the Berlin Blockade, which cut off all non-Soviet food, water and other supplies for the citizens of the non-Soviet sectors of Berlin. Because Berlin was located within the Soviet-occupied zone of Germany, the only available methods of supplying the city were three limited air corridors. A massive aerial supply campaign was initiated by the United States, Britain, France, and other countries, the success of which caused the Soviets to lift their blockade in May 1949.