There was a sort of cargo carrying submarine that was part of the story in a science fiction book that I read a very long time ago. I can not remember the title or the author.
The submarine was actually a tug that pulled a very large submarine oil barge. The submarine tug was armed with a number of torpedoes and drones located around the exterior of the hull. The plot had something to do with moving the oil from a disputed area back to the United States and it involved a long submarine tunnel that exited into the Gulf of Mexico. All very fantastic from the descriptions in the book.