I would bet US SONAR picks them up as soon as they power up.
I would bet US SONAR picks them up as soon as they power up.
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I’m sure it would depend on distance, depth, and speed. I have no idea from what these subs are constructed, but it’s possible that they have sound-absorbent materials on the hull. When you don’t have to put a crew onboard, they can be made pretty small too. I’d be interested in how much one of these costs to produce.