In addition, vast distances to targets challenged the skill and endurance of its aircrews. Although SAC operated the B-36 intercontinental bomber to strike anywhere in the world, it initiated the development of an aerial refueling capability in fall 1947. In 1948 it adopted the British hose method, converting some piston-engine B-29s to tankers, and formed two aerial refueling squadrons in June 1948. SAC later adopted the Boeing flying boom method of refueling, made standard in 1958. Using four aerial refuelings, the B-50 Lucky Lady II flew nonstop around the world between February 26 and March 2, 1949, to demonstrate the technique's global strike potential. Destined to serve Air Force jet bombers and fighters for the next four decades and beyond, the jet turbine-powered KC-135 Stratotanker, became operational in 1957.
The crisis that precipitated the Berlin Airlift began on June 24, 1948. It revolved around American plans for rebuilding a separate West German state and led the Soviet Union to initiate a ground blockade of the Western-controlled zones of Berlin, 90 miles inside Soviet-controlled East Germany. Forcing the blockade would have required the West to launch a general mobilization, fire first shots, and possibly set off another global war. Although the United States had deployed the conventional B-29 to Europe, perhaps in a calculated bluff that relied on the aircraft's reputation as an atomic delivery vehicle, the crisis continued. The Allies saw an opportunity to resupply Berlin and feed its 2.5 million beleaguered inhabitants by air through three air corridors guaranteed by agreement with the Soviet Union. Lieutenant General Curtis LeMay, then commanding U.S. Air Forces in Europe (USAFE), pieced together an airlift force of C-47 Skytrains left over from World War II, but the 80 tons per day they supplied were not enough. On July 30, 1948, Major General William Tunner, who had run the Himalayan "Hump" airlift during the war, replaced LeMay, the combat leader. Reinforced with four-engine C-54 Skymasters and C-74 Globe-masters, Tunner initiated around-the-clock flights guided by ground control approach radar. His aircraft land- ed every three minutes, carrying a record capacity of 5,620 tons per day. When the airlift appeared to succeed, the Soviet Union threatened to interfere with it.
President Truman responded by sending a wing of B-29s, widely described in the world press at the time as "atomic" bombers, to England. They were not, but the Soviet Union apparently believed they were and made no move to interrupt the airlift. In May 1949 it provided the United States with the first victory of the Cold War (without a shot being fired) when, after eleven months, 277,000 flights, and 2.3 million tons of life-sustaining supplies, it opened Berlin to surface traffic. A few months