The ongoing dispute over Berlin strained relations between the Soviet Union and the Western Allies (United States, United Kingdom, France). On 24 June 1948, the Soviet Union blocked access to the three Western-held sectors of Berlin, which lay deep within the Soviet-controlled zone of Germany, by cutting off all rail and road routes going through Soviet-controlled territory in Germany. The commander of the American occupation zone in Germany, General Lucius D. Clay, USA, gave the order on 25 June to launch a massive airlift using both civil and military aircraft. Rhein-Main Air Base became the main American terminal in western Germany for the airlift. The aircraft of the 61st TCG participated using C-54 Skymasters to ferry coal, flour, and other cargo into West Berlin. Additional Troop Carrier Squadrons were assigned to the 61st group, these being the 20th, 48th, and 54th.