In nuclear strategy, a first strike or preemptive strike is a preemptive surprise attack employing overwhelming force. First strike capability is a country's ability to defeat another nuclear power by destroying its arsenal to the point where the attacking country can survive the weakened retaliation while the opposing side is left unable to continue war. The preferred methodology is to attack the opponent's strategic nuclear weapon facilities (missile silos, submarine bases, bomber airfields), command and control sites, and storage depots first. The strategy is called counterforce. Historical background First-strike attack, the use of a nuclear first strike capability, was greatly feared during the Cold War between NATO and the Soviet Bloc. At various points, fear of a first strike attack existed on both sides. Misunderstood changes in posture and well understood changes in technology used by either side often led to speculation regarding the enemy's intentions. 1948–1961 In the immediate aftermath of World War II, the leadership of the Soviet Union feared the United States would use its nuclear superiority to its advantage, as from 1945 to 1948 the U.S. was the only state possessing nuclear weapons. The USSR countered by rapidly developing their own nuclear weapons, surprising the US with their first test in 1949. In turn, the U.S. countered by developing the vastly more powerful thermonuclear weapon, testing their first hydrogen bomb in 1952 at Ivy Mike, but the USSR quickly countered by testing their own thermonuclear weapons, with a test in 1953 of a semi-thermonuclear weapon of the Sloika design, and in 1956, with the testing of Sakharov's Third Idea – equivalent to the Castle Bravo device. Meanwhile, tensions between the two nations rose as 1956 saw the suppression of Hungary by the Soviets; the U.S. and European nations drew certain conclusions from that event, while in the U.S., a powerful social backlash was afoot, prompted by Senator Joseph McCarthy, the House Un-American Activities Committee, and Julius and Ethel Rosenberg, U.S. citizens executed in 1953 after conviction of espionage. This atmosphere was further inflamed by the 1957 launch of Sputnik, which led to fears of Communists attacking from outer space, as well as concerns that if the Soviets could launch a device into orbit, they could equally cause a device to re-enter the atmosphere and impact any part of the planet. John F. Kennedy capitalized on this situation by emphasizing the bomber gap and the missile gap,