I'd think that towing anything in violent weather would be dangerous. If self propelled rather than towed your idea becomes a merchant submarine. That would have to greatly complicate things and be slower and/or use much more fuel.
It doesn't have to be underwater to be either towable or self propelled. See the other comment about barges on the Mississippi for towing and SpaceX's "of course I still love you" (and friends) for self propelled.
Autonomous and underwater would be hard, radio doesn't travel well through water.
They're not only common on the Mississippi, but also the Rhine area in the Netherlands and Germany as hinterland operations for the port of Rotterdam, as well as the Danube area in eastern Europe.
Both self-propelled barges and push barges have been used for ages already in inland shipping in Europe, but have not been used a lot in the rest of the world. They also seem to only be suitable for river transport. With small scale transport over sea you have so-called feeder ships, which have an entirely different build, and never push extra barges/ships.
No, I mean autonomous too. Autonomous vehicles still want access to GPS, you still want to know where your stuff is, you still want to be able to give new orders if something changes, etc.
