The podcast series 'Blowback' on the history of US-Cuban relations has an episode about the Cuban missile crisis. In this episode the hosts state that in the early 60s Khrushchev was given info from Soviet intelligence that the US had been planning a premptive nuclear attack on the Soviet union, and that they had called off this attack after a Soviet nuclear test showed their capabilities to be beyond what the us had believed. This led Khrushchev to believe it a sensible deterrent strategy to place nuclear weapons in Cuba. What the podcast didn't cover was whether or not this Intel wass accurate so I thought I'd ask here. Was the us actually planning a premptive strike on the Soviet union? If so what were these plans? If not why did Soviet intelligence believe this?
The US always had — and probably still has — contingency plans for first-strike nuclear attacks on its major adversaries, and certainly had them in the late 1950s and early 1960s. But the US was also aware that by the late 1950s, the Soviet retaliatory capability was such that the US could not expect to avoiding losing certainly its European allies, but also at least a few of its own major cities.
The idea that the US "called off" its plans on the basis of Soviet nuclear testing is nonsense. The US did watch Soviet nuclear capabilities very closely, and certainly believed that by the early 1960s the Soviets had achieved essentially "parity" with the United States with respects to the design of high-yield nuclear weapons (but not yet low-yield ones). But that was part of what they predicted what was going to happen from the early 1950s onward.
Separately, we have a pretty good idea of what led Khrushchev to put nukes in Cuba, and this isn't it. He wanted nukes in Cuba as a counterbalance to US nukes in Turkey and Western Europe, to use to possibly apply more leverage on the Berlin situation, and to serve as an insurance policy against a future US invasion of Cuba.
Anyway, I don't know what intelligence Khrushchev received, but the idea that Soviet nuclear tests in the early 1960s made the US stop a plan in motion is nonsense. The US did have first-strike contingency plans — but that doesn't mean they were actually planning to use them. By the mid-1950s the USSR already had a capacity to destroy Western Europe and that was not something the US was interested in having happen if it could be avoided.