[Whitebeard]

I have, I also know that it is a game of 'If I was going to do this how would I'.

There are a lot smarter Marine engineer want to be out there, and all it will take is someone wanting to make a good score. The problems are this, Sub cost money to run, and can need a large infrastructure to keep running.

Granted, the cost can be defrayed by the profit on the delivery, but consider

pilot, and making sure they and the crew keep mouth shut.
Cost of fuel
upkeep on seals, batteries, navigations systems, normal wear and tear.
Ability to move change the delivery locations.
16 hours at 1.5 knots
1.5 knots is 1.72 mph roughly. 1.72 x 16 hours is 27 miles distance. Not a money winner.


The better option is a false keel, or a tow behind below the water surface