I remember reading an article (That I cannot seem to find at the moment) about US border agents stopping a Cartel submarine dead in its tracks. What they found is a minimalistic submarine, capable of transporting a small load of product to a destination. They've found other submarines that have sunk due to their bad quality.
I think we're confusing actual military submarines with a makeshift version.
I found their software engineering to be much more advanced than their submarines.