If they are electric they have to charge their batteries. To do that they need air for some sort of generator. Air equals snorkels and snorkels can be seen both visually and with advanced radar. Then comes the means of propulsion. Any blade make a noise that our subs can find, catalog and track. Each one has a signature.
I doubt if maybe 10% are deployed at any one time except for the show of force drills they like to have. So with that said, the sub pens are known because we have followed them there, again, cataloging everyone of them. Despite all of the hand wringing by dupes of the caliber of Wallace, we are getting nothing more than the surrender crowd trying to deter any action because they believe all of the garbage coming out of NK but have no idea of what we are capable of, or even worse, try to project their wadded panty fears to elicit doing nothing to wish for peace without strength.
I remember hearing similar things from people in my unit back before the invasion of Iraq. I remember hearing about “easy combat pay” and “just like desert storm”. I was against that invasion. I’m not in favor of this one either. I worry more about the likes of Chuck Schumer, Elizabeth Warren, and Nancy Pelosi than Kim Jong-un. They all made out pretty well after Iraq.