There is decent post on CIMSEC looking at the possibility of terrorists using the vehicles developed by drug smugglers to carry out an attack. The author also does a pretty good job of explaining why smugglers might be unlikely to cooperate. There is also a worthwhile bibliography associated with the post that appears to have been an academic treatise.
Chuck Hill's CG Blog
Chuck Hill's CG Blog 
Very interesting article, thanks, passing it on to some folks
The blowback from the use of a submarine in a terror attack would be I think fairly massive – but that still leaves a Cole like attack – a plain 40 ft power boat bought off Craigs List could be packed with a lot of explosives and then remote controlled with probably off the shelf parts in the U.S. – Run it alongside a cruise ship and push the boom button. Or could be done while fueling in a port with the fuel barge rafted along side. Remember nobody needs to die for terror to work. Might also be able to put something under the ship at the pier, bury it in the mud and hope kthe security divers miss the addition, and the list goes on and on.
Submarines are hard, but self propelled semi-submersibles, remote controlled or with suicidal operators, are relatively easy and almost invisible in the dark.
The SPSS – more accurately, a low profile vessel, in that the typical SPSS doesn’t dive like a true submarine – has been around since 1993. For the past 25 years, analysts and strategists have been writing hand wringing “what if” articles like the current CIMSEC piece. And yet, there has been no credible evidence to suggest that an SPSS has EVER been used to commit a terrorist act.
Why is that? Probably because there are far easier conveyances available for terrorists to utilize. Anyone who has ever been inside one knows just how crude and dangerous to the operator they truly are.
Are they a potential threat? Sure. But they aren’t the “doomsday” threat some like to claim they are.