In the United States, during the Cold War, the missile gap was the perceived superiority of the number and power of the USSR's missiles in comparison with those of the U.S. (a lack of military parity). The gap in the ballistic missile arsenals did not exist except in exaggerated estimates, made by the Gaither Committee in 1957 and in United States Air Force (USAF) figures. Even the contradictory CIA figures for the USSR's weaponry, which showed a clear advantage for the US, were far above the actual count. Like the bomber gap of only a few years earlier, it was soon demonstrated that the gap was entirely fictional.
John F. Kennedy is credited with inventing the term in 1958 as part of the ongoing election campaign in which a primary plank of his rhetoric was that the Eisenhower administration was weak on defense. It was later learned that Kennedy was apprised of the actual situation during the campaign, which has led scholars to question what Kennedy knew and when he knew it. There has been some speculation that he was aware of the illusory nature of the missile gap from the start and that he was using it solely as a political tool, an example of policy by press release.
Background
The Soviet launch of Sputnik 1, on October 4, 1957, highlighted the technological achievements of the Soviets and sparked some worrying questions for the politicians and general public of the US. Although US military and civilian agencies were well aware of Soviet satellite plans, as they were publicly announced as part of the International Geophysical Year, US President Dwight Eisenhower's announcements that the event was unsurprising found little support among a US public that was still struggling with McCarthyism.
Political opponents seized on the event, helped by Eisenhower's ineffectual response, as further proof that the US was "fiddling as Rome burned." Senator John F. Kennedy stated "the nation was losing the satellite-missile race with the Soviet Union because of… complacent miscalculations, penny-pinching, budget cutbacks, incredibly confused mismanagement, and wasteful rivalries and jealousies." The Soviets capitalized on their strengthened position with false claims of Soviet missile capabilities, claiming on December 4, 1958, "Soviet ICBMs are at present in mass production." Five days later, Soviet Premier Nikita Khrushchev boasted the successful testing of an ICBM with an impressive range. Coupled with the US's failed launch of the Titan ICBM (Inter Continental Ballistic Missile) that month, a sense of Soviet superiority in missile technology became prevalent.
Discrepancy between intelligence and information made public
National Intelligence Estimate (NIE) 11-10-57, issued in December 1957, predicted that the Soviets would "probably have a first operational capability with up to 10 prototype ICBMs" at "some time during the period from mid-1958 to mid-1959." The numbers started to inflate.
A similar report gathered only a few months later, NIE 11-5-58, released in August 1958, concluded that the USSR had "the technical and industrial capability... to have an operational capability with 100 ICBMs" some time in 1960 and perhaps 500 ICBMs "some time in 1961, or at the latest in 1962."
However, senior U.S. leadership knew these estimates of existing Soviet missile capabilities were completely inaccurate. Beginning with the collection of photo-intelligence by high-altitude U-2 overflights of the Soviet Union in 1956, the Eisenhower administration had increasingly-hard evidence that strategic weapons estimates favoring the Soviets were false. The CIA placed the number of ICBMs to be closer to a dozen. Continued sporadic flights failed to turn up any evidence of additional missiles. But the White House and the CIA wished to protect the secrecy of the source of the information--the photographs captured by the U-2 flying in illegal violation of Soviet airspace--and so they continued to hide the more accurate information that there were nearly zero Soviet ICBMs deployed. They kept the American public in the dark even though they knew from the start that the Soviets were monitoring the U-2 overflights. On the very day of the first U-2 overflight the Soviet ambassador to Washington protested the high-altitude violation of Soviet airspace, a fact denied by Washington and reported on by the press.
Curtis LeMay argued that the large stocks of missiles were in the areas not photographed by the U-2s, and arguments broke out over the Soviet factory capability, in an effort to estimate their production rate.