Never said it was - If memory serves I think it was a nuclear powered conventionally armed submarine with the capability of destroying any potential invasion force with conventional weapons. It might have been conventionally powered but that's not the issue. My point being if your opponent knows...
Well if all of the 195 countries had rational governments with a basic understanding of self preservation yes it is a convincing argument and everyone would be safer, but back in the real world we have the non proliferation treaty.
Who ever thought or claimed nuclear weapons could prevent...