This has been tried several times in the past. Some shipments do make it in, since they 'sub' is much harder to see with a limited superstructure. What concerns me is if these dicks figure out how to run a true sub, and attempt this.
You can buy old subs from the tourist industry and covert it internally to carry for the right money. Repaint, and reconfigure the breathing system to recirculate, and scrub. Then you need a captain, who is used to running the same boat. The problem will be distances, most of the tourist version are not set up as long distance travel. But this too can be worked on.
Tourist Submarines - Deepstar Used Tourist Sub
Certification - ABS A1
Operating depth - 100 m
Passengers - 45
Crew - 2
Length - 19 m
Beam - 4 m
Pressure hull diameter - 2.2 m
Draft - 3.1 m
Weight in air - 90 tons
Side viewports - acrylic cylinders
Bow viewports - 2.2 m.
Maximum surface speed - 3 knots
Submerged cruise speed - 1 knot
Maximum submerged speed - 3 knots
Main thrusters - 2 x 7.5 KW
Vertical thrusters - 2 x 7.5 KW
Bow thruster - 1 x 7.5 KW
Stern thruster - 1 x 7.5 KW
Submerged endurance - 16hours @ 1.5 knots
Main oxygen - 7251 @200 bar
Main air - 18751@245 bar
Main battery - 240 VDC
Emergency battery - 24 VDC
Battery capacity - 420 KWH
Battery charging time - 10 hours
Main ballast capacity - 10,000 kg
Variable ballast - 4,000 kg
Trim/drop weight - 4,000 kg
Normal dive life support - 24 hours for 47 passengers
Emergency life support - 72 hours for 47 passengers
CO2 absorbent - Sofnolime
Air conditioning - 33,000 BTU/hour
Compass main - magnetic fluxgate
Speed log - digital
Depth gauge - digital and analog
Active sonar - colour imaging
Surface communications - VHF radio
Subsurface UWT - 27KHZ
Not the fastest on the market......and it will be noisy as hell.