The only threat they pose is to some other third-rate navy or shipping vessels that are pretty much running blind. If push comes to shove they will become underwater reefs very quickly.
You might be a bit optimistic. Even old subs can be deadly; just like an elderly cobra, it's venom still works.
Then again I might not be, having spent quite a bit of time on one during my stint in the Navy. We played lots of war games with diesel boats, diesel boats a hell of a lot better than the ones we are talking about here. And we ate their lunch every day of the week, even in an old 637 class boat that was far from top of the line, even 20 years ago. I know somewhat of what I am talking about you see, having been there, done that.
