>>520199522
Dunno. Probably it gets spiked during Solar Winds too. Probably they gathered enough data already.

What military was interested at time, was demolishing potential at ground level. Meaning, industrial and decision-making centers. For those, underground tests works good enough. I guess.
At that time, sattelite tech was underdeveloped. Doubt that they were worrying about spikes of ionization in Van Allen belt then.