Just a thought experiment, let’s say the earth is flat, looks like many professionals would know, including
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Pilots/ATC/sea captain
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Land surveyor and civil engineers
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Astronomers and Geologists, at least the one dealing with experimental data
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Militaries, at least radar operator and artillery
Just these categories are already a lot of persons, I assume I miss a lot of others. So how many person does it make in total ? 10 % of the population ?
Wasn’t the Manhattan project compromised from within because of communist sympathizers, or even outright communists working on the project?
Correct, though that wasn’t the only leak, just the most serious.