There is a new publication that appears to be the definitive source on Narco subs and related craft including semi-submersibles and un-manned, towed narco “torpedoes.” It certainly has the best selection of photographs I have ever seen on the subject.
Narco-Submarines Specially Fabricated Vessels Used For Drug Smuggling Purposes
In cooperation with InSight Crime & Small Wars Journal— El Centro
Byron Ramirez and Robert J. Bunker, Editors
And of course these could be used for smuggling in things other than drugs.
You can access the report in pdf form here.
http://www.informationdissemination.net/ which has been providing excellent coverage of the crisis in Korea, also found a piece of particular interest to the Coast Guard in Der Spiegel (in English) recounting an interview with a man purported to have piloted vessels smuggling cocaine North for two years including semi-submersibles.
It makes interesting reading.
More photos of the narco-sub and the “shipyard” where it was built here.
This article has a bit more information but the most interesting part is an almost 30 minute video (in Spanish with English subtitles) about development of semi-submersibles and towed submersible cargo containers. It includes comments by both the Captain commanding the Colombian Coast Guard in the Pacific and a “retired” drug smuggler. Be aware there are commercials, but I recommend it highly. (Ex-WMEC-628 Durable, transferred in 2003, is visible in many of the scenes from the Colombian base.)