Rear-cockpit ‘hybrid narco-sub’ had been intercepted by the USCG cutter Mohawk on 3rd July 2018. Photo by Petty Officer 3rd Class Brandon Murray, USCG
Covert Shores provides the latest in a series, looking at the craft used by drug smugglers in recent interdictions, with particular emphasis on the emergence of hybrid, high-speed, cockpit aft, outboard powered craft.
Not exactly the typical low profile self propelled semi-submersible, but definitely low observable if they are not making a visible wake. Maybe their tactic is a combination of sprint and drift?
Chuck Hill's CG Blog 
US Navy appears to have a Grand Total of ONE Semi-Submersible Vessel called the CCH (Combatant Craft Heavy) “Sealion”. Approximately 80-feet long by ~14.5-feet breadth by ~9.5-feet from keel to Deck House Ceiling, Dry Weight ~65,000-pounds and a Wet Weight of ~80,000-pounds. Accommodations Seven…
Some info hear. http://www.hisutton.com/SEALION%20and%20Alligator%20stealth%20boats.html
They also have fully submersible swimmer delivery vehicles.
Yeah, but a Narco Sub isn’t a Submarine. Not that the Drug Cartels haven’t considered building their own Submarine Force…