Fair points, Thiel
Some of these boats can dive fairly deep (a couple hundred feet) and have ranges over 1,000 miles, but those are fairly rare. What I'm kinda thinking is a semi-sub slips into the shipping lane and saddles up next to a frieghter and...Boom. I mean, not every merchant ship has patrol aircraft, right?
Or they can use a speed boat, divers, an ultra light, hide it in the cargo, subvert some of the crew, mine the approaches to a harbour, etc etc.
Semi-subs are a threat, but they are far far down on the list.
It's also worth considering that you need specialists workers, tools and materiel to build these boats. That means infrastructure which is traceable and a level of planning and coordination that'll stand out like bull on a bowling lane.
And I really doubt if the Cartels would be interested in selling their boats. Leaving aside the fact that they need them themselves, they're not interested in destabilizing their biggest market and they certainly don't want the kind of attention they'd get from the US if it became known that they'd been providing the boats.
And lastly, cheap is a relative term. Certainly, they're a lot cheaper than a modern submarine, but then they aren't modern submarines either.
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