From a documentary I watched something like this is one of the preferred techniques for the Colombian cartels now. It's called the torpedo technique. They desi

From a documentary I watched something like this is one of the preferred techniques for the Colombian cartels now. It's called the torpedo technique. They design torpedo style units that get towed behind a fishing boat or such. At a desired location they detach it, and it just loiters below the surface. At some pre-arranged time it pops up to the surface and activates a radio beacon, so that a pickup ship can snag it. It's less complicated than building an autonomous AUV, and far less likely to be spotted by arial surveillance than a narcosub. Lower capacity but still very lucrative I imagine. And very nearly risk free.