Why I'm interested in semi-submersibles built by narco trafficers:
They're built in clandestine low-tech shipyards located in the jungles of Colombia. In some cases, they're built with minimal electricity, using mostly hand tools. [2]
Many are one-offs, and are scuttled once they reach their destination.
So many one-off semi-submersibles are being built that independent organizations have formed to provide sub-building services to the drug cartels. There exist people with specialized knowledge in building low-tech semi-submersibles in the jungle.
Typical specs (for the type of semi-submersible I'm building)