[hga]

Yields didn't really increase that much, there's a limiting factor where more and more of the energy released simply radiates out into space, and that's somewhere around 1MT as I recall.

A serious, concrete underground "hideout" will save you from anything but a really close hit; I can look up numbers if you want, but I maybe remember a good metric is 1MT and one mile of separation, requiring a less intense shelter. And a large fraction of the population can get by with much less, carpet bombing suburbia and exurbia was never going to happen, especially due to counterforce requirements and the Soviets believing that MAD was profoundly immoral and never buying into it.