My husband was a first grader in SC in the early 60’s and was told to get under the desk, do not look at the light. If strange people came in, took away the teacher and the flag, just do what the replacement teacher said. Funny thing, he lived in the center of a 100 mile diameter area that included Charleston nuclear sub base, the Atomic Energy Commission Savannah River site (where they made the bombs), Fort Jackson military training base, Shaw airforce base (Shaw took the photos of Cuba), and McEntire national guard base. He found out years later that the Russian bombs were so inaccurate that they sent numerous ones at each target. He still wonders where the strange people and the new teacher would have come from! LOL
I worked in a Naval plant that repaired and aligned the guidence systems for ICBMs on our subs.
It was a given that we’d see no flash, as our nervous system doesn’t work that fast.