So, the Colombian organizations figured there had to be a safer way to transport the drugs. That's how the idea of the semi-submersible was born, without a clear understanding of how they were going to work. The first semi-submersible that was interdicted was found off the Caribbean coast in 1993. From then on they have evolved. They've improved their design, aerodynamics and, of course, their capacity. To date, Colombian authorities have interdicted or captured 36 semi-submersibles, both in open sea and in the estuaries.
Those are sub-standard ships, and their designs are not commercially available. Basically if you take away their top you can see that it has the body of an old cigarette go-fast boat. They've increased their depth, they've covered them, and they've added pipes for the crew to breath and for the engine exhaust. Because of their design one fourth of the semi-submersible remains above the surface.
Currently, construction time is between 35 and 45 days, and in the bigger makeshift shipyards, they build up to 3 or 4 at the same time. All the workshops are in the jungles of Buenaventura. That's where all the semi-submersibles of Colombia were and are still built. The roads to get there are inaccessible in many cases. The area is protected, in part, by FARC guerrillas and, in part, by the paramilitaries.
Colombian Narcosubs - Criminal documentary